[original post is not on my news server]
[Doron Tal]
>>> > Recently I tried to execute a python file using execfile (exec
>>> > performed just the same for that reason).
Not over here:
Python 2.4.4 (#2, Aug 1 2008, 00:04:43)
[GCC 4.1.3 20070929 (prerelease) (Ubuntu 4.1.2-16ubuntu2)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> def f():
... execfile("execme.py")
... print "locals:", locals()
... print a
...
>>> f()
locals: {'a': 2}
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "<stdin>", line 4, in f
NameError: global name 'a' is not defined
>>> def g():
... exec open("execme.py").read()
... print "locals:", locals()
... print a
...
>>> g()
locals: {'a': 2}
2
The reason is that while execfile() is just an ordinary function the exec
statement affects the function's bytecode (LOAD_NAME instead of LOAD_GLOBAL
or LOAD_FAST). This leads to the following Voodoo:
>>> def h():
... exec ""
... execfile("execme.py")
... print "locals:", locals()
... print a
...
>>> h()
locals: {'a': 2}
2
While this is certainly not the most regular behaviour it allows to avoid
going through a dictionary for every assignment in functions that don't
have an exec statement, thus giving you faster code in the vast majority of
cases at the cost of a few quirks like the one you encountered.
Peter
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