Added two new questions; about globals/locals and about recursive imports.

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Guido van Rossum 1996-07-30 18:53:05 +00:00
parent 63d9cd708f
commit 0d20cfa108
1 changed files with 40 additions and 6 deletions

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@ -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
===================