Re: confused about the different built-in functions in Python
snip On 5/25/14 7:55 PM, Deb Wyatt wrote: I am confused about how various built-in functions are called. Some are called with dot notation snip How do you know/remember which way to call them? TIA, Deb in WA, USA It can be confusing. Generally, built-in functions (like sum, len, etc) are used when the operation could apply to many different types. For example, sum() can be used with any iterable that produces addable things. Operations that are defined only for a single type (like .isalpha as a string operation) are usually defined as methods on the type. This is not a black/white distinction, I'm sure there are interesting counter-examples. But this is the general principle. -- Ned Batchelder, http://nedbatchelder.com -- https://mail.python.org/mailman/listinfo/python-list Thank you for answering. I meant to send this to the tutor list, but messed up. So, I guess there isn't a magic answer to this one, and I'll learn as I learn the language. Have a great day. Deb in WA, USA FREE 3D EARTH SCREENSAVER - Watch the Earth right on your desktop! Check it out at http://www.inbox.com/earth -- https://mail.python.org/mailman/listinfo/python-list
Re: confused about the different built-in functions in Python
On 5/26/2014 11:15 AM, Deb Wyatt wrote: snip On 5/25/14 7:55 PM, Deb Wyatt wrote: I am confused about how various built-in functions are called. Some are called with dot notation snip How do you know/remember which way to call them? It can be confusing. Generally, built-in functions (like sum, len, etc) are used when the operation could apply to many different types. For example, sum() can be used with any iterable that produces addable things. Operations that are defined only for a single type (like .isalpha as a string operation) are usually defined as methods on the type. This is not a black/white distinction, I'm sure there are interesting counter-examples. But this is the general principle. Part of the answer is Python's history. Up to about 2.1, most built-in types did not have methods, though I know lists did. Ints and strings did not, or chr and ord might have been int.chr() and str.ord(). (The current string methods were originally functions in the string module.) Thank you for answering. I meant to send this to the tutor list, but messed up. So, I guess there isn't a magic answer to this one, and I'll learn as I learn the language. Have a great day. -- Terry Jan Reedy -- https://mail.python.org/mailman/listinfo/python-list
Re: confused about the different built-in functions in Python
Terry Reedy tjre...@udel.edu: Part of the answer is Python's history. Up to about 2.1, most built-in types did not have methods, though I know lists did. Ints and strings did not, or chr and ord might have been int.chr() and str.ord(). (The current string methods were originally functions in the string module.) Ints still aren't quite like regular objects. For example: x = 500 x.__str__ is x.__str__ False Marko -- https://mail.python.org/mailman/listinfo/python-list
Re: confused about the different built-in functions in Python
On 26.05.2014 21:00, Marko Rauhamaa wrote: Terry Reedy tjre...@udel.edu: Part of the answer is Python's history. Up to about 2.1, most built-in types did not have methods, though I know lists did. Ints and strings did not, or chr and ord might have been int.chr() and str.ord(). (The current string methods were originally functions in the string module.) Ints still aren't quite like regular objects. For example: x = 500 x.__str__ is x.__str__ False Just like every other object: class Example(object): pass ... e = Example() e.__str__ is e.__str__ False Python creates a new bound method object every time. A bound method object is a callable object that keeps a strong reference to the function, class and object. The bound method object adds the object as first argument to the function (aka 'self'). Christian -- https://mail.python.org/mailman/listinfo/python-list
Re: confused about the different built-in functions in Python
Christian Heimes christ...@python.org: Python creates a new bound method object every time. A bound method object is a callable object that keeps a strong reference to the function, class and object. The bound method object adds the object as first argument to the function (aka 'self'). I stand corrected. I had thought the trampoline (bound method object) was created once and for all. Marko -- https://mail.python.org/mailman/listinfo/python-list
Re: confused about the different built-in functions in Python
Marko Rauhamaa ma...@pacujo.net: Christian Heimes christ...@python.org: Python creates a new bound method object every time. A bound method object is a callable object that keeps a strong reference to the function, class and object. The bound method object adds the object as first argument to the function (aka 'self'). I stand corrected. I had thought the trampoline (bound method object) was created once and for all. Sure enough. The principle is explicitly specified in URL: https://docs.python.org/3.2/reference/datamodel.html#index-46. Thus: class X: ... def f(self): ... print(Hello) ... x = X() x.f() Hello def f(): print(Meh) ... x.f = f x.f() Meh delattr(x, f) x.f() Hello IOW, you can override a method with setattr() but you cannot delete a method with delattr(). Marko -- https://mail.python.org/mailman/listinfo/python-list
Re: confused about the different built-in functions in Python
Marko Rauhamaa wrote: IOW, you can override a method with setattr() but you cannot delete a method with delattr(). Actually, you can -- but you need to delete it from the class, not the instance: delattr(X, 'f') x.f() Traceback (most recent call last): File stdin, line 1, in module AttributeError: 'X' object has no attribute 'f' -- Greg -- https://mail.python.org/mailman/listinfo/python-list
Re: confused about the different built-in functions in Python
On Mon, 26 May 2014 23:58:37 +0300, Marko Rauhamaa wrote: Marko Rauhamaa ma...@pacujo.net: Christian Heimes christ...@python.org: Python creates a new bound method object every time. A bound method object is a callable object that keeps a strong reference to the function, class and object. The bound method object adds the object as first argument to the function (aka 'self'). I stand corrected. I had thought the trampoline (bound method object) was created once and for all. Sure enough. The principle is explicitly specified in URL: https://docs.python.org/3.2/reference/datamodel.html#index-46. Thus: class X: ... def f(self): ... print(Hello) ... x = X() x.f() Hello def f(): print(Meh) ... x.f = f x.f() Meh delattr(x, f) x.f() Hello IOW, you can override a method with setattr() but you cannot delete a method with delattr(). Of course you can. You just need to know where methods are found. Hint: we write this: class Example: def method(self): ... not this: class Example: def __init__(self): def method(self): ... self.method = method Methods are attributes of the class, not the instance. Like all class attributes, you can retrieve them by doing a lookup on the instance, you can shadow them by storing an attribute of the same name on the instance, but you cannot rebind or delete them directly on the instance, since they aren't on the instance. -- Steven D'Aprano http://import-that.dreamwidth.org/ -- https://mail.python.org/mailman/listinfo/python-list
Re: confused about the different built-in functions in Python
On 5/26/2014 4:32 PM, Marko Rauhamaa wrote: I stand corrected. I had thought the trampoline (bound method object) was created once and for all. Assuming that bound methods are immutable, this is an implementation detail, either way. However, it is common for a specific method to be called just once on a specific instance. If you have a mixed-case string Ss and want the lowercase version, ss = Ss.lower(), you keep ss around as long as needed. If the bound method is needed repeatedly, you can keep *that* around too. stack = [] spush = stack.append spop = stack.pop for item in it: spush(item) while stack and condition: p = process(spop) ... -- Terry Jan Reedy -- https://mail.python.org/mailman/listinfo/python-list
confused about the different built-in functions in Python
I am confused about how various built-in functions are called. Some are called with dot notationeach_item.isalpha()and some are called like 'normal'sum(numlist)How do you know/remember which way to call them?TIA,Deb in WA, USA Free Online Photosharing - Share your photos online with your friends and family! Visit http://www.inbox.com/photosharing to find out more! -- https://mail.python.org/mailman/listinfo/python-list
Re: confused about the different built-in functions in Python
On 5/25/14 7:55 PM, Deb Wyatt wrote: I am confused about how various built-in functions are called. Some are called with dot notation each_item.isalpha() and some are called like 'normal' sum(numlist) How do you know/remember which way to call them? TIA, Deb in WA, USA It can be confusing. Generally, built-in functions (like sum, len, etc) are used when the operation could apply to many different types. For example, sum() can be used with any iterable that produces addable things. Operations that are defined only for a single type (like .isalpha as a string operation) are usually defined as methods on the type. This is not a black/white distinction, I'm sure there are interesting counter-examples. But this is the general principle. -- Ned Batchelder, http://nedbatchelder.com -- https://mail.python.org/mailman/listinfo/python-list
Re: confused about the different built-in functions in Python
On 25May2014 15:55, Deb Wyatt codemon...@inbox.com wrote: I am confused about how various built-in functions are called. Some are called with dot notation each_item.isalpha() and some are called like 'normal' sum(numlist) How do you know/remember which way to call them? Documentation. However, some context: each_item.isalpha() is not a builtin function as such. It is a method of the str class. Whereas sum _is_ a builtin function, a globally known name which can be accessed and used without explicitly importing any module. There's an explicit list of the builtin functions in the Python doco. For a class, you can look at the doco for the class (String methods in the python doco, for the str class), or run: help(str) at the interactive Python prompt. Cheers, Cameron Simpson c...@zip.com.au Steinbach's Law: 2 is not equal to 3 -- even for large values of 2. -- https://mail.python.org/mailman/listinfo/python-list
