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Diffstat (limited to 'Misc/FAQ')
-rw-r--r-- | Misc/FAQ | 46 |
1 files changed, 40 insertions, 6 deletions
@@ -175,6 +175,8 @@ Here's an overview of the questions per chapter: 4.33. Q. Is there an inverse to the format operator (a la C's scanf())? 4.34. Q. Can I have Tk events handled while waiting for I/O? 4.35. Q. How do I write a function with output parameters (call by reference)? + 4.36. Q. Please explain the rules for local and global variables in Python. + 4.37. Q. How can I have modules that mutually import each other? 5. Extending Python 5.1. Q. Can I create my own functions in C? @@ -1243,12 +1245,8 @@ with native look and feel on NT, Windows 3.1 (using win32s) and on Unix (using Tk). Source and binaries for NT and Linux are available in <URL:ftp://ftp.python.org/pub/python/wpy>. -- Python has been mentioned on the "Futurism" subpage of the Fresco -home page <URL:http://www.faslab.com/fresco/HomePage.html>. "Pesto" -is a Python interface to the CORBA dynamic invocation interface, and -thus Fresco. A Pesto prototype is running and is currently being -packaged up for inclusion in the Fresco snapshot. See also the Pesto -web pages: <URL:http://www.faslab.com/fresco/pesto/Index.html>. +- (The Fresco port that was mentioned in earlier versions of this FAQ +no longer seems to exist. Inquire with Mark Linton.) 4.14. Q. Are there any interfaces to database packages in Python? @@ -1696,6 +1694,42 @@ in a number of ways: [Python' author favors solution 3 in most cases.] +4.36. Q. Please explain the rules for local and global variables in Python. + +A. [Ken Manheimer] In Python, procedure variables are implicitly +global, unless they assigned anywhere within the block. In that case +they are implicitly local, and you need to explicitly declare them as +'global'. + +Though a bit surprising at first, a moments consideration explains +this. On one hand, requirement of 'global' for assigned vars provides +a bar against unintended side-effects. On the other hand, if global +were required for all global references, you'd be using global all the +time. Eg, you'd have to declare as global every reference to a +builtin function, or to a component of an imported module. This +clutter would defeat the usefulness of the 'global' declaration for +identifying side-effects. + +4.37. Q. How can I have modules that mutually import each other? + +A. Jim Roskind recommends the following order in each module: + +First: all exports (like globals, functions, and classes that don't +need imported bases classes). + +Then: all import statements. + +Finally: all active code (including globals that are initialized from +imported values). + +Python's author doesn't like this approach much because the imports +appear in a strange place, but has to admit that it works. His +recommended strategy is to avoid all uses of "from <module> import *" +(so everything from an imported module is referenced as +<module>.<name>) and to place all code inside functions. +Initializations of global variables and class variables should use +constants or built-in functions only. + 5. Extending Python =================== |