Re: Scoping Issues
Andrew Berg wrote: On 5/24/2012 8:59 PM, Dave Angel wrote: so I fixed that, and got inconsistent use of tabs and spaces in indentation because you mistakenly used tabs for indentation. Not to start another tabs-vs.-spaces discussion, Too late, the seeds of war have been planted, we reached to point of no return. The OP mistakenly used spaces with its tabs for indentation. JM -- http://mail.python.org/mailman/listinfo/python-list
Re: Scoping Issues
Andrew Berg wrote: On 5/24/2012 8:59 PM, Dave Angel wrote: so I fixed that, and got inconsistent use of tabs and spaces in indentation because you mistakenly used tabs for indentation. Not to start another tabs-vs.-spaces discussion, but tabs are perfectly legal indentation in Python. That exception is raised when the interpreter can't determine how much a line is indented because tabs and spaces are both used. To be clear: each entire suite must be consistent with its use of either tabs /or/ spaces -- attempting to use both, even on seperate lines, raises `TabError: inconsistent use of tabs and spaces in indentation`. (Python 3, of course. ;) ~Ethan~ -- http://mail.python.org/mailman/listinfo/python-list
Scoping Issues
def adder(): s = 0 def a(x): s += x return sum return a pos, neg = adder(), adder() for i in range(10): print pos(i), neg(-2*i) This should work, right? Why does it not? Checkout slide no. 37 of a Tour of Go to know inspiration. Just wanted to see if python was the same as Go in this regard. Sorry, if I'm being rude, or anything. -- http://mail.python.org/mailman/listinfo/python-list
Re: Scoping Issues
On 25/05/2012 02:23, SherjilOzair wrote: def adder(): s = 0 def a(x): s += x return sum return a pos, neg = adder(), adder() for i in range(10): print pos(i), neg(-2*i) This should work, right? Why does it not? Checkout slide no. 37 of a Tour of Go to know inspiration. Just wanted to see if python was the same as Go in this regard. Sorry, if I'm being rude, or anything. If you bind to a name (assign to a variable) in a function, that name is by default local to the function unless it's declared as global (which means in this module's namespace) or nonlocal (which means in the enclosing function's namespace) (Python 3 only). -- http://mail.python.org/mailman/listinfo/python-list
Re: Scoping Issues
On Thu, 24 May 2012 18:23:18 -0700, SherjilOzair wrote: def adder(): s = 0 def a(x): s += x return sum return a I think you mean return s, not sum. This should work, right? Why does it not? No, it shouldn't. When you have an assignment, such as s += x, Python treats s as a local variable. Since s is local to the inner function a(), it has no initial value, and the += fails. In Python 3, you can declare s to be a non-local variable with the nonlocal keyword: def adder(): s = 0 def a(x): nonlocal s s += x return s return a which now works the way you should expect: add = adder() add(1) 1 add(2) 3 add(5) 8 But in Python 2, which you are using, there is no nonlocal keyword and you can only write to globals (declaring them with the global keyword) or locals (with no declaration), not nonlocals. There are a number of work-arounds to this. One is to use a callable class: class Adder: def __init__(self): self.s = 0 def __call__(self, x): self.s += x return self.s Another is to use an extra level of indirection, and a mutable argument. Instead of rebinding the non-local, you simply modify it in place: def adder(): s = [0] def a(x): s[0] += x return s[0] return a -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: Scoping Issues
On Thu, May 24, 2012 at 6:23 PM, SherjilOzair sherjiloz...@gmail.com wrote: def adder(): s = 0 def a(x): Add a nonlocal s declaration right here. See http://www.python.org/dev/peps/pep-3104/ s += x return sum return a pos, neg = adder(), adder() for i in range(10): print pos(i), neg(-2*i) This should work, right? Why does it not? Python doesn't have a C-like variable declaration scheme. So without a `global` or `nonlocal` declaration, you can only assign to names which reside in the innermost scope. Checkout slide no. 37 of a Tour of Go to know inspiration. You mean slide #38 (And functions are full closures.). Just wanted to see if python was the same as Go in this regard. Sorry, if I'm being rude, or anything. I would suggest reading through the Python Language Reference (http://docs.python.org/release/3.1.5/reference/index.html ) prior to asking further questions, as it may well answer them for you. Cheers, Chris -- http://mail.python.org/mailman/listinfo/python-list
Re: Scoping Issues
On 05/24/2012 09:23 PM, SherjilOzair wrote: def adder(): s = 0 def a(x): s += x return sum return a pos, neg = adder(), adder() for i in range(10): print pos(i), neg(-2*i) This should work, right? Why does it not? Guess that depends on what you mean by work. First, it gets a syntax error on the print function call, because you omitted the parens. When I fixed that, I got UnboundLocalError: local variable 's' referenced before assignment so I fixed that, and got inconsistent use of tabs and spaces in indentation because you mistakenly used tabs for indentation. Then I got the output built-in function sum built-in function sum because sum is a built-in function. Presumably you meant to return s, not sum. Here's what I end up with, and it seems to work fine in Python 3.2 on Linux: def adder(): s = 0 def a(x): nonlocal s s += x return s return a pos, neg = adder(), adder() for i in range(10): print (pos(i), neg(-2*i)) . Output is: 0 0 1 -2 3 -6 6 -12 10 -20 15 -30 21 -42 28 -56 36 -72 45 -90 -- DaveA -- http://mail.python.org/mailman/listinfo/python-list
Re: Scoping Issues
On 5/24/2012 8:59 PM, Dave Angel wrote: so I fixed that, and got inconsistent use of tabs and spaces in indentation because you mistakenly used tabs for indentation. Not to start another tabs-vs.-spaces discussion, but tabs are perfectly legal indentation in Python. That exception is raised when the interpreter can't determine how much a line is indented because tabs and spaces are both used. -- CPython 3.3.0a3 | Windows NT 6.1.7601.17790 -- http://mail.python.org/mailman/listinfo/python-list
Re: Scoping Issues
On 05/24/2012 10:27 PM, Andrew Berg wrote: On 5/24/2012 8:59 PM, Dave Angel wrote: so I fixed that, and got inconsistent use of tabs and spaces in indentation because you mistakenly used tabs for indentation. Not to start another tabs-vs.-spaces discussion, but tabs are perfectly legal indentation in Python. That exception is raised when the interpreter can't determine how much a line is indented because tabs and spaces are both used. I configure my editor(s) to always use spaces for indentation. So a file that currently uses tabs is unusable to me. You of course are right that tabs are syntactically correct, but until I find another editor that makes tabs visible (like the one I used 20 years ago) they're unacceptable to me. -- DaveA -- http://mail.python.org/mailman/listinfo/python-list
