Re: Argh!! Can't wrap my head around this Python stuff!

[nospam . nospam . nospam . bartc]

On 26/11/2017 09:09, Greg Tibbet wrote:
>
> I'm an old timer, have programmed in Fortran, C, C++, Perl, and a bit
> of Java and trying to learn this new-fangled Python language!
>
> I've got a small program that uses PIL to create an image, draw some
> primitives (rectanges, ellipses, etc...) and save it.  Works fine...
> no issues.
>
> I've found in the past, the best way to "really learn" the language
> was to "dig into the guts" and understand it,.. I thought I was making
> progress, but when looking into the PIL library to see what's going on
> behind the scenes, I find the following code in ImageDraw.py
>
> def ellipse(self, xy, fill=None, outline=None):
>  """Draw an ellipse."""
>  ink, fill = self._getink(outline, fill)
>  if fill is not None:
>  self.draw.draw_ellipse(xy, fill, 1)
> <...snipped...>
>
> ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
> but WHERE is draw_ellipse defined??  What magic is happening there?
> I've searched the entire PIL directory tree, and the ONLY two places
> draw_ellipse is mentioned are right there in the ellipse() function...
> WHAT am I missing??

Python isn't a very pure language in that much of the functionality that looks
like it should be written in Python (because you imported a module just like
you import any Python module), actually is written in something else, as has
been pointed out.

It's reasonable that some things need to be implemented using some foreign
functions. But the boundary between Python and non-Python is blurred.

Take this program:

  import sys

and try and find sys.py in your installation.

(This is an obstacle if, for example, you're thinking of implementing a Python
interpreter. In theory, once you have it working, it should run any .py
program. But the critical modules it needs don't have .py source code. And the
interface to those non-Python functions isn't defined with special byte-code
instructions.

(It will be done /via/ those instructions, but the magic needed is on the other
 side of them. Calling into sys.fn() uses the same CALL_FUNCTION byte-code as
calling into a regular Python function.)

As I said, it's not pure. More of a jungle as you've found out.)

--
bartc

-- 
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Re: Argh!! Can't wrap my head around this Python stuff!

[nospam . nospam . nospam . Wanderer]

On Sunday, November 26, 2017 at 4:10:12 AM UTC-5, Greg Tibbet wrote:
> I'm an old timer, have programmed in Fortran, C, C++, Perl, and a bit
> of Java and trying to learn this new-fangled Python language!
>
> I've got a small program that uses PIL to create an image, draw some
> primitives (rectanges, ellipses, etc...) and save it.  Works fine...
> no issues.
>
> I've found in the past, the best way to "really learn" the language
> was to "dig into the guts" and understand it,.. I thought I was making
> progress, but when looking into the PIL library to see what's going on
> behind the scenes, I find the following code in ImageDraw.py
>
> def ellipse(self, xy, fill=None, outline=None):
> """Draw an ellipse."""
> ink, fill = self._getink(outline, fill)
> if fill is not None:
> self.draw.draw_ellipse(xy, fill, 1)
> <...snipped...>
>
> ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
> but WHERE is draw_ellipse defined??  What magic is happening there?
> I've searched the entire PIL directory tree, and the ONLY two places
> draw_ellipse is mentioned are right there in the ellipse() function...
> WHAT am I missing??
>
> Thanks!
> -Stumpy (aka Greg)

I'm googlesmart when it comes to Python. I used to know C. I practically knew
what the assembly language would look like when it compiled. There was no
internet and searching through books can be really laborious so you almost had
to really know it to use it. But with Python, I don't start from first
principles. I google what I want to do, download the appropriate packages and
read through the examples. It can be really frustrating when you get bugs,
because you don't know what's going on deep down in the code.

-- 
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Re: Argh!! Can't wrap my head around this Python stuff!

[Stefan Ram]

Ram) (Stefan Ram)

Greg Tibbet  writes:
>I'm an old timer, have programmed in Fortran, C, C++, Perl, and a bit
>of Java and trying to learn this new-fangled Python language!

  Which actually is older than Java.

>def ellipse(self, xy, fill=None, outline=None):
>"""Draw an ellipse."""
>ink, fill = self._getink(outline, fill)
>if fill is not None:
>self.draw.draw_ellipse(xy, fill, 1)
><...snipped...>
>ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
>but WHERE is draw_ellipse defined??  What magic is happening there?

  Depends on the nature of â»selfâ«.

  Usually, the answer would be that it's defined in a superclass.

  But with Python, one could also decrypt a string and then feed
  the result to â»execâ« to dynamically add methods to an object
  whose source code is well hidden.

  Looking into the matter, it turns out, however, ...

  â»_draw_ellipseâ« is defined in the language C in the file
  â»_imaging.câ« and then mapped to â»draw_ellipseâ« via PyMethodDef
  which is part of Python's C API.

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Re: Argh!! Can't wrap my head around this Python stuff!

[nospam . nospam . bartc]

On 26/11/2017 09:09, Greg Tibbet wrote:
>
> I'm an old timer, have programmed in Fortran, C, C++, Perl, and a bit
> of Java and trying to learn this new-fangled Python language!
>
> I've got a small program that uses PIL to create an image, draw some
> primitives (rectanges, ellipses, etc...) and save it.  Works fine...
> no issues.
>
> I've found in the past, the best way to "really learn" the language
> was to "dig into the guts" and understand it,.. I thought I was making
> progress, but when looking into the PIL library to see what's going on
> behind the scenes, I find the following code in ImageDraw.py
>
> def ellipse(self, xy, fill=None, outline=None):
>  """Draw an ellipse."""
>  ink, fill = self._getink(outline, fill)
>  if fill is not None:
>  self.draw.draw_ellipse(xy, fill, 1)
> <...snipped...>
>
> ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
> but WHERE is draw_ellipse defined??  What magic is happening there?
> I've searched the entire PIL directory tree, and the ONLY two places
> draw_ellipse is mentioned are right there in the ellipse() function...
> WHAT am I missing??

Python isn't a very pure language in that much of the functionality that looks
like it should be written in Python (because you imported a module just like
you import any Python module), actually is written in something else, as has
been pointed out.

It's reasonable that some things need to be implemented using some foreign
functions. But the boundary between Python and non-Python is blurred.

Take this program:

  import sys

and try and find sys.py in your installation.

(This is an obstacle if, for example, you're thinking of implementing a Python
interpreter. In theory, once you have it working, it should run any .py
program. But the critical modules it needs don't have .py source code. And the
interface to those non-Python functions isn't defined with special byte-code
instructions.

(It will be done /via/ those instructions, but the magic needed is on the other
 side of them. Calling into sys.fn() uses the same CALL_FUNCTION byte-code as
calling into a regular Python function.)

As I said, it's not pure. More of a jungle as you've found out.)

--
bartc

-- 
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Re: Argh!! Can't wrap my head around this Python stuff!

[nospam . nospam . Wanderer]

On Sunday, November 26, 2017 at 4:10:12 AM UTC-5, Greg Tibbet wrote:
> I'm an old timer, have programmed in Fortran, C, C++, Perl, and a bit
> of Java and trying to learn this new-fangled Python language!
>
> I've got a small program that uses PIL to create an image, draw some
> primitives (rectanges, ellipses, etc...) and save it.  Works fine...
> no issues.
>
> I've found in the past, the best way to "really learn" the language
> was to "dig into the guts" and understand it,.. I thought I was making
> progress, but when looking into the PIL library to see what's going on
> behind the scenes, I find the following code in ImageDraw.py
>
> def ellipse(self, xy, fill=None, outline=None):
> """Draw an ellipse."""
> ink, fill = self._getink(outline, fill)
> if fill is not None:
> self.draw.draw_ellipse(xy, fill, 1)
> <...snipped...>
>
> ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
> but WHERE is draw_ellipse defined??  What magic is happening there?
> I've searched the entire PIL directory tree, and the ONLY two places
> draw_ellipse is mentioned are right there in the ellipse() function...
> WHAT am I missing??
>
> Thanks!
> -Stumpy (aka Greg)

I'm googlesmart when it comes to Python. I used to know C. I practically knew
what the assembly language would look like when it compiled. There was no
internet and searching through books can be really laborious so you almost had
to really know it to use it. But with Python, I don't start from first
principles. I google what I want to do, download the appropriate packages and
read through the examples. It can be really frustrating when you get bugs,
because you don't know what's going on deep down in the code.

-- 
https://mail.python.org/mailman/listinfo/python-list

Re: Argh!! Can't wrap my head around this Python stuff!

[nospam . nospam . Cameron Simpson]

On 26Nov2017 01:09, Greg Tibbet  wrote:
>I've got a small program that uses PIL to create an image, draw some
>primitives (rectanges, ellipses, etc...) and save it.  Works fine...
>no issues.
>
>I've found in the past, the best way to "really learn" the language
>was to "dig into the guts" and understand it,.. I thought I was making
>progress, but when looking into the PIL library to see what's going on
>behind the scenes, I find the following code in ImageDraw.py
>
>def ellipse(self, xy, fill=None, outline=None):
>"""Draw an ellipse."""
>ink, fill = self._getink(outline, fill)
>if fill is not None:
>self.draw.draw_ellipse(xy, fill, 1)
><...snipped...>
>
>ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
>but WHERE is draw_ellipse defined??  What magic is happening there?
>I've searched the entire PIL directory tree, and the ONLY two places
>draw_ellipse is mentioned are right there in the ellipse() function...
>WHAT am I missing??

"ellispse()" is a method in the ImageDraw class. Looking at the __init__ method
 of that class we see:

  self.draw = Image.core.draw(self.im, blend)

so "self.draw" in your code above is the result of "Image.core.draw(self.im,
blend)". "Image" is the Image module imported at the top of ImageDraw.py. So we
 hop over to Image.py, which has this code:

try:
# If the _imaging C module is not present, you can still use
# the "open" function to identify files, but you cannot load
# them.  Note that other modules should not refer to _imaging
# directly; import Image and use the Image.core variable instead.
import _imaging
core = _imaging
del _imaging
except ImportError, v:
core = _imaging_not_installed()
if str(v)[:20] == "Module use of python" and warnings:
# The _imaging C module is present, but not compiled for
# the right version (windows only).  Print a warning, if
# possible.
warnings.warn(
"The _imaging extension was built for another version "
"of Python; most PIL functions will be disabled",
RuntimeWarning
)

Now the import works (because you'd get exceptions otherwise), so code which
matters is that the top of that:

import _imaging
core = _imaging
del _imaging

So "core" is a reference to the "_imaging" module (and the name "_imaging" has
been discarded). So... The name Image.core is now a reference to that module.

So back in ImageDraw, the call to "Image.core.draw()" called the function
"draw" from the _imaging module, which presumably returns some kind of drawing
object, and _that_ object has a "draw_ellispe" method.

Now, dynamic languages like Python don't lend themselves to screamingly fast
compute, so expensive stuff like drawing graphics is usually done by hooking
into special purpose libraries written in C or something that compiles to
efficient machine level code (C++, Go, what have you).

You can ship C code with Python to be compiled on the target and presented to
Python as a library, and by convention such modules are named with a leading
underscore. So we can expect that _imaging is a C code module.

And if you go up a level you'll find _imaging.c, with a draw_ellipse function
inside it.

Cheers,
Cameron Simpson  (formerly c...@zip.com.au)

-- 
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Re: Argh!! Can't wrap my head around this Python stuff!

[nospam . nospam . Peter Otten]

Greg Tibbet wrote:

>
> I'm an old timer, have programmed in Fortran, C, C++, Perl, and a bit
> of Java and trying to learn this new-fangled Python language!
>
> I've got a small program that uses PIL to create an image, draw some
> primitives (rectanges, ellipses, etc...) and save it.  Works fine...
> no issues.
>
> I've found in the past, the best way to "really learn" the language
> was to "dig into the guts" and understand it,.. I thought I was making
> progress, but when looking into the PIL library to see what's going on
> behind the scenes, I find the following code in ImageDraw.py
>
> def ellipse(self, xy, fill=None, outline=None):
> """Draw an ellipse."""
> ink, fill = self._getink(outline, fill)
> if fill is not None:
> self.draw.draw_ellipse(xy, fill, 1)
> <...snipped...>
>
> ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
> but WHERE is draw_ellipse defined??  What magic is happening there?
> I've searched the entire PIL directory tree, and the ONLY two places
> draw_ellipse is mentioned are right there in the ellipse() function...
> WHAT am I missing??

The first argument of ellipse(), self is a strong hint that it is a method. If
you look into ImageDraw.py, located at

>>> import PIL.ImageDraw
>>> PIL.ImageDraw.__file__
'/usr/lib/python3/dist-packages/PIL/ImageDraw.py'

on my machine, you'll find the class of the same name, ImageDraw, and in its
initializer there's an assignment to the self.draw attribute:

self.draw = Image.core.draw(self.im, blend)

Image is another module

>>> PIL.ImageDraw.Image


and if you look for the name 'core' in that module you'll find

from PIL import _imaging as core

>>> PIL.ImageDraw.Image.core


That would be the right time to say "Argh" with any number of exclamation marks
 for those who don't know C, but since you are familiar with that language
there's nothing to stop you from downloading the PIL (or rather the pillow)
source and look into the implementation. Once you have the complete code

https://pypi.python.org/pypi/Pillow/4.3.0
https://python-pillow.org/
https://github.com/python-pillow/Pillow
$ git clone https://github.com/python-pillow/Pillow.git

...you can use traditional tools:

$ find Pillow/ -name \*.c -print0 | xargs -0 grep draw_ellipse
Pillow/_imaging.c:_draw_ellipse(ImagingDrawObject* self, PyObject* args)
Pillow/_imaging.c:{"draw_ellipse", (PyCFunction)_draw_ellipse, 1},

Rinse and repeat ;)

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Re: Argh!! Can't wrap my head around this Python stuff!

[nospam . nospam . Gisle Vanem]

Greg Tibbet wrote:

> ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
> but WHERE is draw_ellipse defined??  What magic is happening there?
> I've searched the entire PIL directory tree, and the ONLY two places
> draw_ellipse is mentioned are right there in the ellipse() function...
> WHAT am I missing??

The C sources. Not all of PIL is ritten in Python.

draw_ellipse() is a thin wrapper for ImagingDrawEllips(). See PIL/_imaging.c:
   https://github.com/python-pillow/Pillow/_imaging.c

Which again is in libimage/Draw.c:
   https://github.com/python-pillow/Pillow/blob/13d84993717cffd64a2e1d7e3e6edb1
85973d559/libImaging/Draw.c

calling ellipse().

--
--gv

-- 
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Re: Argh!! Can't wrap my head around this Python stuff!

[Stefan Ram]

Greg Tibbet  writes:
>I'm an old timer, have programmed in Fortran, C, C++, Perl, and a bit
>of Java and trying to learn this new-fangled Python language!

  Which actually is older than Java.

>def ellipse(self, xy, fill=None, outline=None):
>"""Draw an ellipse."""
>ink, fill = self._getink(outline, fill)
>if fill is not None:
>self.draw.draw_ellipse(xy, fill, 1)
><...snipped...>
>ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
>but WHERE is draw_ellipse defined??  What magic is happening there?

  Depends on the nature of â»selfâ«.

  Usually, the answer would be that it's defined in a superclass.

  But with Python, one could also decrypt a string and then feed
  the result to â»execâ« to dynamically add methods to an object
  whose source code is well hidden.

  Looking into the matter, it turns out, however, ...

  â»_draw_ellipseâ« is defined in the language C in the file
  â»_imaging.câ« and then mapped to â»draw_ellipseâ« via PyMethodDef
  which is part of Python's C API.

-- 
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Argh!! Can't wrap my head around this Python stuff!

[nospam . nospam . Greg Tibbet]

I'm an old timer, have programmed in Fortran, C, C++, Perl, and a bit of Java
and trying to learn this new-fangled Python language!

I've got a small program that uses PIL to create an image, draw some primitives
 (rectanges, ellipses, etc...) and save it.  Works fine... no issues.

I've found in the past, the best way to "really learn" the language was to "dig
 into the guts" and understand it,.. I thought I was making progress, but when
looking into the PIL library to see what's going on behind the scenes, I find
the following code in ImageDraw.py

def ellipse(self, xy, fill=None, outline=None):
"""Draw an ellipse."""
ink, fill = self._getink(outline, fill)
if fill is not None:
self.draw.draw_ellipse(xy, fill, 1)
<...snipped...>

ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
but WHERE is draw_ellipse defined??  What magic is happening there? I've
searched the entire PIL directory tree, and the ONLY two places draw_ellipse is
 mentioned are right there in the ellipse() function... WHAT am I missing??

Thanks!
-Stumpy (aka Greg)

-- 
https://mail.python.org/mailman/listinfo/python-list

Re: Argh!! Can't wrap my head around this Python stuff!

[nospam . bartc]

On 26/11/2017 09:09, Greg Tibbet wrote:
>
> I'm an old timer, have programmed in Fortran, C, C++, Perl, and a bit
> of Java and trying to learn this new-fangled Python language!
>
> I've got a small program that uses PIL to create an image, draw some
> primitives (rectanges, ellipses, etc...) and save it.  Works fine...
> no issues.
>
> I've found in the past, the best way to "really learn" the language
> was to "dig into the guts" and understand it,.. I thought I was making
> progress, but when looking into the PIL library to see what's going on
> behind the scenes, I find the following code in ImageDraw.py
>
> def ellipse(self, xy, fill=None, outline=None):
>  """Draw an ellipse."""
>  ink, fill = self._getink(outline, fill)
>  if fill is not None:
>  self.draw.draw_ellipse(xy, fill, 1)
> <...snipped...>
>
> ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
> but WHERE is draw_ellipse defined??  What magic is happening there?
> I've searched the entire PIL directory tree, and the ONLY two places
> draw_ellipse is mentioned are right there in the ellipse() function...
> WHAT am I missing??

Python isn't a very pure language in that much of the functionality that looks
like it should be written in Python (because you imported a module just like
you import any Python module), actually is written in something else, as has
been pointed out.

It's reasonable that some things need to be implemented using some foreign
functions. But the boundary between Python and non-Python is blurred.

Take this program:

  import sys

and try and find sys.py in your installation.

(This is an obstacle if, for example, you're thinking of implementing a Python
interpreter. In theory, once you have it working, it should run any .py
program. But the critical modules it needs don't have .py source code. And the
interface to those non-Python functions isn't defined with special byte-code
instructions.

(It will be done /via/ those instructions, but the magic needed is on the other
 side of them. Calling into sys.fn() uses the same CALL_FUNCTION byte-code as
calling into a regular Python function.)

As I said, it's not pure. More of a jungle as you've found out.)

--
bartc

-- 
https://mail.python.org/mailman/listinfo/python-list

Re: Argh!! Can't wrap my head around this Python stuff!

[nospam . Peter Otten]

Greg Tibbet wrote:

>
> I'm an old timer, have programmed in Fortran, C, C++, Perl, and a bit
> of Java and trying to learn this new-fangled Python language!
>
> I've got a small program that uses PIL to create an image, draw some
> primitives (rectanges, ellipses, etc...) and save it.  Works fine...
> no issues.
>
> I've found in the past, the best way to "really learn" the language
> was to "dig into the guts" and understand it,.. I thought I was making
> progress, but when looking into the PIL library to see what's going on
> behind the scenes, I find the following code in ImageDraw.py
>
> def ellipse(self, xy, fill=None, outline=None):
> """Draw an ellipse."""
> ink, fill = self._getink(outline, fill)
> if fill is not None:
> self.draw.draw_ellipse(xy, fill, 1)
> <...snipped...>
>
> ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
> but WHERE is draw_ellipse defined??  What magic is happening there?
> I've searched the entire PIL directory tree, and the ONLY two places
> draw_ellipse is mentioned are right there in the ellipse() function...
> WHAT am I missing??

The first argument of ellipse(), self is a strong hint that it is a method. If
you look into ImageDraw.py, located at

>>> import PIL.ImageDraw
>>> PIL.ImageDraw.__file__
'/usr/lib/python3/dist-packages/PIL/ImageDraw.py'

on my machine, you'll find the class of the same name, ImageDraw, and in its
initializer there's an assignment to the self.draw attribute:

self.draw = Image.core.draw(self.im, blend)

Image is another module

>>> PIL.ImageDraw.Image


and if you look for the name 'core' in that module you'll find

from PIL import _imaging as core

>>> PIL.ImageDraw.Image.core


That would be the right time to say "Argh" with any number of exclamation marks
 for those who don't know C, but since you are familiar with that language
there's nothing to stop you from downloading the PIL (or rather the pillow)
source and look into the implementation. Once you have the complete code

https://pypi.python.org/pypi/Pillow/4.3.0
https://python-pillow.org/
https://github.com/python-pillow/Pillow
$ git clone https://github.com/python-pillow/Pillow.git

...you can use traditional tools:

$ find Pillow/ -name \*.c -print0 | xargs -0 grep draw_ellipse
Pillow/_imaging.c:_draw_ellipse(ImagingDrawObject* self, PyObject* args)
Pillow/_imaging.c:{"draw_ellipse", (PyCFunction)_draw_ellipse, 1},

Rinse and repeat ;)

-- 
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Re: Argh!! Can't wrap my head around this Python stuff!

[nospam . Cameron Simpson]

On 26Nov2017 01:09, Greg Tibbet  wrote:
>I've got a small program that uses PIL to create an image, draw some
>primitives (rectanges, ellipses, etc...) and save it.  Works fine...
>no issues.
>
>I've found in the past, the best way to "really learn" the language
>was to "dig into the guts" and understand it,.. I thought I was making
>progress, but when looking into the PIL library to see what's going on
>behind the scenes, I find the following code in ImageDraw.py
>
>def ellipse(self, xy, fill=None, outline=None):
>"""Draw an ellipse."""
>ink, fill = self._getink(outline, fill)
>if fill is not None:
>self.draw.draw_ellipse(xy, fill, 1)
><...snipped...>
>
>ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
>but WHERE is draw_ellipse defined??  What magic is happening there?
>I've searched the entire PIL directory tree, and the ONLY two places
>draw_ellipse is mentioned are right there in the ellipse() function...
>WHAT am I missing??

"ellispse()" is a method in the ImageDraw class. Looking at the __init__ method
 of that class we see:

  self.draw = Image.core.draw(self.im, blend)

so "self.draw" in your code above is the result of "Image.core.draw(self.im,
blend)". "Image" is the Image module imported at the top of ImageDraw.py. So we
 hop over to Image.py, which has this code:

try:
# If the _imaging C module is not present, you can still use
# the "open" function to identify files, but you cannot load
# them.  Note that other modules should not refer to _imaging
# directly; import Image and use the Image.core variable instead.
import _imaging
core = _imaging
del _imaging
except ImportError, v:
core = _imaging_not_installed()
if str(v)[:20] == "Module use of python" and warnings:
# The _imaging C module is present, but not compiled for
# the right version (windows only).  Print a warning, if
# possible.
warnings.warn(
"The _imaging extension was built for another version "
"of Python; most PIL functions will be disabled",
RuntimeWarning
)

Now the import works (because you'd get exceptions otherwise), so code which
matters is that the top of that:

import _imaging
core = _imaging
del _imaging

So "core" is a reference to the "_imaging" module (and the name "_imaging" has
been discarded). So... The name Image.core is now a reference to that module.

So back in ImageDraw, the call to "Image.core.draw()" called the function
"draw" from the _imaging module, which presumably returns some kind of drawing
object, and _that_ object has a "draw_ellispe" method.

Now, dynamic languages like Python don't lend themselves to screamingly fast
compute, so expensive stuff like drawing graphics is usually done by hooking
into special purpose libraries written in C or something that compiles to
efficient machine level code (C++, Go, what have you).

You can ship C code with Python to be compiled on the target and presented to
Python as a library, and by convention such modules are named with a leading
underscore. So we can expect that _imaging is a C code module.

And if you go up a level you'll find _imaging.c, with a draw_ellipse function
inside it.

Cheers,
Cameron Simpson  (formerly c...@zip.com.au)

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Re: Argh!! Can't wrap my head around this Python stuff!

[nospam . Wanderer]

On Sunday, November 26, 2017 at 4:10:12 AM UTC-5, Greg Tibbet wrote:
> I'm an old timer, have programmed in Fortran, C, C++, Perl, and a bit
> of Java and trying to learn this new-fangled Python language!
>
> I've got a small program that uses PIL to create an image, draw some
> primitives (rectanges, ellipses, etc...) and save it.  Works fine...
> no issues.
>
> I've found in the past, the best way to "really learn" the language
> was to "dig into the guts" and understand it,.. I thought I was making
> progress, but when looking into the PIL library to see what's going on
> behind the scenes, I find the following code in ImageDraw.py
>
> def ellipse(self, xy, fill=None, outline=None):
> """Draw an ellipse."""
> ink, fill = self._getink(outline, fill)
> if fill is not None:
> self.draw.draw_ellipse(xy, fill, 1)
> <...snipped...>
>
> ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
> but WHERE is draw_ellipse defined??  What magic is happening there?
> I've searched the entire PIL directory tree, and the ONLY two places
> draw_ellipse is mentioned are right there in the ellipse() function...
> WHAT am I missing??
>
> Thanks!
> -Stumpy (aka Greg)

I'm googlesmart when it comes to Python. I used to know C. I practically knew
what the assembly language would look like when it compiled. There was no
internet and searching through books can be really laborious so you almost had
to really know it to use it. But with Python, I don't start from first
principles. I google what I want to do, download the appropriate packages and
read through the examples. It can be really frustrating when you get bugs,
because you don't know what's going on deep down in the code.

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Re: Argh!! Can't wrap my head around this Python stuff!

[nospam . Gisle Vanem]

Greg Tibbet wrote:

> ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
> but WHERE is draw_ellipse defined??  What magic is happening there?
> I've searched the entire PIL directory tree, and the ONLY two places
> draw_ellipse is mentioned are right there in the ellipse() function...
> WHAT am I missing??

The C sources. Not all of PIL is ritten in Python.

draw_ellipse() is a thin wrapper for ImagingDrawEllips(). See PIL/_imaging.c:
   https://github.com/python-pillow/Pillow/_imaging.c

Which again is in libimage/Draw.c:
   https://github.com/python-pillow/Pillow/blob/13d84993717cffd64a2e1d7e3e6edb1
85973d559/libImaging/Draw.c

calling ellipse().

--
--gv

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Re: Argh!! Can't wrap my head around this Python stuff!

[Stefan Ram]

Greg Tibbet  writes:
>I'm an old timer, have programmed in Fortran, C, C++, Perl, and a bit
>of Java and trying to learn this new-fangled Python language!

  Which actually is older than Java.

>def ellipse(self, xy, fill=None, outline=None):
>"""Draw an ellipse."""
>ink, fill = self._getink(outline, fill)
>if fill is not None:
>self.draw.draw_ellipse(xy, fill, 1)
><...snipped...>
>ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
>but WHERE is draw_ellipse defined??  What magic is happening there?

  Depends on the nature of â»selfâ«.

  Usually, the answer would be that it's defined in a superclass.

  But with Python, one could also decrypt a string and then feed
  the result to â»execâ« to dynamically add methods to an object
  whose source code is well hidden.

  Looking into the matter, it turns out, however, ...

  â»_draw_ellipseâ« is defined in the language C in the file
  â»_imaging.câ« and then mapped to â»draw_ellipseâ« via PyMethodDef
  which is part of Python's C API.

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Re: Argh!! Can't wrap my head around this Python stuff!

[nospam . Vincent Vande Vyvre]

Le 26/11/17 Ä  10:09, Greg Tibbet a ÄCcritâ :
> I'm an old timer, have programmed in Fortran, C, C++, Perl, and a bit
> of Java and trying to learn this new-fangled Python language!
>
> I've got a small program that uses PIL to create an image, draw some
> primitives (rectanges, ellipses, etc...) and save it.  Works fine...
> no issues.
>
> I've found in the past, the best way to "really learn" the language
> was to "dig into the guts" and understand it,.. I thought I was making
> progress, but when looking into the PIL library to see what's going on
> behind the scenes, I find the following code in ImageDraw.py
>
> def ellipse(self, xy, fill=None, outline=None):
>  """Draw an ellipse."""
>  ink, fill = self._getink(outline, fill)
>  if fill is not None:
>  self.draw.draw_ellipse(xy, fill, 1)
> <...snipped...>
>
> ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
> but WHERE is draw_ellipse defined??  What magic is happening there?
> I've searched the entire PIL directory tree, and the ONLY two places
> draw_ellipse is mentioned are right there in the ellipse() function...
> WHAT am I missing??
>
> Thanks!
> -Stumpy (aka Greg)

Hi,

It's not defined in Python module but in
Pillow-3.5/Pillow-master/libImaging/Draw.c

... line 748


Vincent

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Argh!! Can't wrap my head around this Python stuff!

[nospam . Greg Tibbet]

I'm an old timer, have programmed in Fortran, C, C++, Perl, and a bit of Java
and trying to learn this new-fangled Python language!

I've got a small program that uses PIL to create an image, draw some primitives
 (rectanges, ellipses, etc...) and save it.  Works fine... no issues.

I've found in the past, the best way to "really learn" the language was to "dig
 into the guts" and understand it,.. I thought I was making progress, but when
looking into the PIL library to see what's going on behind the scenes, I find
the following code in ImageDraw.py

def ellipse(self, xy, fill=None, outline=None):
"""Draw an ellipse."""
ink, fill = self._getink(outline, fill)
if fill is not None:
self.draw.draw_ellipse(xy, fill, 1)
<...snipped...>

ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
but WHERE is draw_ellipse defined??  What magic is happening there? I've
searched the entire PIL directory tree, and the ONLY two places draw_ellipse is
 mentioned are right there in the ellipse() function... WHAT am I missing??

Thanks!
-Stumpy (aka Greg)

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Re: Argh!! Can't wrap my head around this Python stuff!

[Wanderer]

On Sunday, November 26, 2017 at 4:10:12 AM UTC-5, Greg Tibbet wrote:
> I'm an old timer, have programmed in Fortran, C, C++, Perl, and a bit
> of Java and trying to learn this new-fangled Python language!
> 
> I've got a small program that uses PIL to create an image, draw some
> primitives (rectanges, ellipses, etc...) and save it.  Works fine...
> no issues.
> 
> I've found in the past, the best way to "really learn" the language
> was to "dig into the guts" and understand it,.. I thought I was making
> progress, but when looking into the PIL library to see what's going on
> behind the scenes, I find the following code in ImageDraw.py
> 
> def ellipse(self, xy, fill=None, outline=None):
> """Draw an ellipse."""
> ink, fill = self._getink(outline, fill)
> if fill is not None:
> self.draw.draw_ellipse(xy, fill, 1)
> <...snipped...>
> 
> ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
> but WHERE is draw_ellipse defined??  What magic is happening there?
> I've searched the entire PIL directory tree, and the ONLY two places
> draw_ellipse is mentioned are right there in the ellipse() function...
> WHAT am I missing??  
> 
> Thanks!
> -Stumpy (aka Greg)

I'm googlesmart when it comes to Python. I used to know C. I practically knew 
what the assembly language would look like when it compiled. There was no 
internet and searching through books can be really laborious so you almost had 
to really know it to use it. But with Python, I don't start from first 
principles. I google what I want to do, download the appropriate packages and 
read through the examples. It can be really frustrating when you get bugs, 
because you don't know what's going on deep down in the code.
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Re: Argh!! Can't wrap my head around this Python stuff!

[Vincent Vande Vyvre]

Le 26/11/17 à 10:09, Greg Tibbet a écrit :

I'm an old timer, have programmed in Fortran, C, C++, Perl, and a bit
of Java and trying to learn this new-fangled Python language!

I've got a small program that uses PIL to create an image, draw some
primitives (rectanges, ellipses, etc...) and save it.  Works fine...
no issues.

I've found in the past, the best way to "really learn" the language
was to "dig into the guts" and understand it,.. I thought I was making
progress, but when looking into the PIL library to see what's going on
behind the scenes, I find the following code in ImageDraw.py

def ellipse(self, xy, fill=None, outline=None):
 """Draw an ellipse."""
 ink, fill = self._getink(outline, fill)
 if fill is not None:
 self.draw.draw_ellipse(xy, fill, 1)
<...snipped...>

ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
but WHERE is draw_ellipse defined??  What magic is happening there?
I've searched the entire PIL directory tree, and the ONLY two places
draw_ellipse is mentioned are right there in the ellipse() function...
WHAT am I missing??

Thanks!
-Stumpy (aka Greg)


Hi,

It's not defined in Python module but in 
Pillow-3.5/Pillow-master/libImaging/Draw.c


... line 748


Vincent

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Re: Argh!! Can't wrap my head around this Python stuff!

[bartc]

On 26/11/2017 09:09, Greg Tibbet wrote:


I'm an old timer, have programmed in Fortran, C, C++, Perl, and a bit
of Java and trying to learn this new-fangled Python language!

I've got a small program that uses PIL to create an image, draw some
primitives (rectanges, ellipses, etc...) and save it.  Works fine...
no issues.

I've found in the past, the best way to "really learn" the language
was to "dig into the guts" and understand it,.. I thought I was making
progress, but when looking into the PIL library to see what's going on
behind the scenes, I find the following code in ImageDraw.py

def ellipse(self, xy, fill=None, outline=None):
 """Draw an ellipse."""
 ink, fill = self._getink(outline, fill)
 if fill is not None:
 self.draw.draw_ellipse(xy, fill, 1)
<...snipped...>

ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
but WHERE is draw_ellipse defined??  What magic is happening there?
I've searched the entire PIL directory tree, and the ONLY two places
draw_ellipse is mentioned are right there in the ellipse() function...
WHAT am I missing??


Python isn't a very pure language in that much of the functionality that 
looks like it should be written in Python (because you imported a module 
just like you import any Python module), actually is written in 
something else, as has been pointed out.


It's reasonable that some things need to be implemented using some 
foreign functions. But the boundary between Python and non-Python is 
blurred.


Take this program:

 import sys

and try and find sys.py in your installation.

(This is an obstacle if, for example, you're thinking of implementing a 
Python interpreter. In theory, once you have it working, it should run 
any .py program. But the critical modules it needs don't have .py source 
code. And the interface to those non-Python functions isn't defined with 
special byte-code instructions.


(It will be done /via/ those instructions, but the magic needed is on 
the other side of them. Calling into sys.fn() uses the same 
CALL_FUNCTION byte-code as calling into a regular Python function.)


As I said, it's not pure. More of a jungle as you've found out.)

--
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Re: Argh!! Can't wrap my head around this Python stuff!

[Cameron Simpson]

On 26Nov2017 01:09, Greg Tibbet  wrote:

I've got a small program that uses PIL to create an image, draw some
primitives (rectanges, ellipses, etc...) and save it.  Works fine...
no issues.

I've found in the past, the best way to "really learn" the language
was to "dig into the guts" and understand it,.. I thought I was making
progress, but when looking into the PIL library to see what's going on
behind the scenes, I find the following code in ImageDraw.py

def ellipse(self, xy, fill=None, outline=None):
   """Draw an ellipse."""
   ink, fill = self._getink(outline, fill)
   if fill is not None:
   self.draw.draw_ellipse(xy, fill, 1)
<...snipped...>

ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
but WHERE is draw_ellipse defined??  What magic is happening there?
I've searched the entire PIL directory tree, and the ONLY two places
draw_ellipse is mentioned are right there in the ellipse() function...
WHAT am I missing??


"ellispse()" is a method in the ImageDraw class. Looking at the __init__ method 
of that class we see:


 self.draw = Image.core.draw(self.im, blend)

so "self.draw" in your code above is the result of "Image.core.draw(self.im, 
blend)". "Image" is the Image module imported at the top of ImageDraw.py. So we 
hop over to Image.py, which has this code:


   try:
   # If the _imaging C module is not present, you can still use
   # the "open" function to identify files, but you cannot load
   # them.  Note that other modules should not refer to _imaging
   # directly; import Image and use the Image.core variable instead.
   import _imaging
   core = _imaging
   del _imaging
   except ImportError, v:
   core = _imaging_not_installed()
   if str(v)[:20] == "Module use of python" and warnings:
   # The _imaging C module is present, but not compiled for
   # the right version (windows only).  Print a warning, if
   # possible.
   warnings.warn(
   "The _imaging extension was built for another version "
   "of Python; most PIL functions will be disabled",
   RuntimeWarning
   )

Now the import works (because you'd get exceptions otherwise), so code which 
matters is that the top of that:


   import _imaging
   core = _imaging
   del _imaging

So "core" is a reference to the "_imaging" module (and the name "_imaging" has 
been discarded). So... The name Image.core is now a reference to that module.  

So back in ImageDraw, the call to "Image.core.draw()" called the function 
"draw" from the _imaging module, which presumably returns some kind of drawing 
object, and _that_ object has a "draw_ellispe" method.


Now, dynamic languages like Python don't lend themselves to screamingly fast 
compute, so expensive stuff like drawing graphics is usually done by hooking 
into special purpose libraries written in C or something that compiles to 
efficient machine level code (C++, Go, what have you).


You can ship C code with Python to be compiled on the target and presented to 
Python as a library, and by convention such modules are named with a leading 
underscore. So we can expect that _imaging is a C code module.


And if you go up a level you'll find _imaging.c, with a draw_ellipse function 
inside it.


Cheers,
Cameron Simpson  (formerly c...@zip.com.au)
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Re: Argh!! Can't wrap my head around this Python stuff!

[Peter Otten]

Greg Tibbet wrote:

> 
> I'm an old timer, have programmed in Fortran, C, C++, Perl, and a bit
> of Java and trying to learn this new-fangled Python language!
> 
> I've got a small program that uses PIL to create an image, draw some
> primitives (rectanges, ellipses, etc...) and save it.  Works fine...
> no issues.
> 
> I've found in the past, the best way to "really learn" the language
> was to "dig into the guts" and understand it,.. I thought I was making
> progress, but when looking into the PIL library to see what's going on
> behind the scenes, I find the following code in ImageDraw.py
> 
> def ellipse(self, xy, fill=None, outline=None):
> """Draw an ellipse."""
> ink, fill = self._getink(outline, fill)
> if fill is not None:
> self.draw.draw_ellipse(xy, fill, 1)
> <...snipped...>
> 
> ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
> but WHERE is draw_ellipse defined??  What magic is happening there?
> I've searched the entire PIL directory tree, and the ONLY two places
> draw_ellipse is mentioned are right there in the ellipse() function...
> WHAT am I missing??

The first argument of ellipse(), self is a strong hint that it is a method.
If you look into ImageDraw.py, located at

>>> import PIL.ImageDraw
>>> PIL.ImageDraw.__file__
'/usr/lib/python3/dist-packages/PIL/ImageDraw.py'

on my machine, you'll find the class of the same name, ImageDraw, and in its 
initializer there's an assignment to the self.draw attribute:

self.draw = Image.core.draw(self.im, blend)

Image is another module

>>> PIL.ImageDraw.Image


and if you look for the name 'core' in that module you'll find

from PIL import _imaging as core

>>> PIL.ImageDraw.Image.core


That would be the right time to say "Argh" with any number of exclamation 
marks for those who don't know C, but since you are familiar with that 
language there's nothing to stop you from downloading the PIL (or rather the 
pillow) source and look into the implementation. Once you have the complete 
code

https://pypi.python.org/pypi/Pillow/4.3.0
https://python-pillow.org/
https://github.com/python-pillow/Pillow
$ git clone https://github.com/python-pillow/Pillow.git

...you can use traditional tools:

$ find Pillow/ -name \*.c -print0 | xargs -0 grep draw_ellipse
Pillow/_imaging.c:_draw_ellipse(ImagingDrawObject* self, PyObject* args)
Pillow/_imaging.c:{"draw_ellipse", (PyCFunction)_draw_ellipse, 1},

Rinse and repeat ;)

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Re: Argh!! Can't wrap my head around this Python stuff!

[Gisle Vanem]

Greg Tibbet wrote:


ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
but WHERE is draw_ellipse defined??  What magic is happening there?
I've searched the entire PIL directory tree, and the ONLY two places
draw_ellipse is mentioned are right there in the ellipse() function...
WHAT am I missing??


The C sources. Not all of PIL is ritten in Python.

draw_ellipse() is a thin wrapper for ImagingDrawEllips().
See PIL/_imaging.c:
  https://github.com/python-pillow/Pillow/_imaging.c

Which again is in libimage/Draw.c:
  
https://github.com/python-pillow/Pillow/blob/13d84993717cffd64a2e1d7e3e6edb185973d559/libImaging/Draw.c

calling ellipse().

--
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Argh!! Can't wrap my head around this Python stuff!

[Greg Tibbet]

I'm an old timer, have programmed in Fortran, C, C++, Perl, and a bit
of Java and trying to learn this new-fangled Python language!

I've got a small program that uses PIL to create an image, draw some
primitives (rectanges, ellipses, etc...) and save it.  Works fine...
no issues.

I've found in the past, the best way to "really learn" the language
was to "dig into the guts" and understand it,.. I thought I was making
progress, but when looking into the PIL library to see what's going on
behind the scenes, I find the following code in ImageDraw.py

def ellipse(self, xy, fill=None, outline=None):
"""Draw an ellipse."""
ink, fill = self._getink(outline, fill)
if fill is not None:
self.draw.draw_ellipse(xy, fill, 1)
<...snipped...>

ellipse() uses the method  self.draw.draw_ellipse()   Okay, fine...
but WHERE is draw_ellipse defined??  What magic is happening there?
I've searched the entire PIL directory tree, and the ONLY two places
draw_ellipse is mentioned are right there in the ellipse() function...
WHAT am I missing??  

Thanks!
-Stumpy (aka Greg)
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