[ python-Bugs-1153622 ] eval does not bind variables in lambda bodies correctly

[SourceForge.net]

Bugs item #1153622, was opened at 2005-02-28 11:48
Message generated for change (Comment added) made by tjreedy
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1153622&group_id=5470

Category: Parser/Compiler
Group: Python 2.4
Status: Open
Resolution: None
Priority: 5
Submitted By: Mattias Engdegård (yorick)
Assigned to: Nobody/Anonymous (nobody)
Summary: eval does not bind variables in lambda bodies correctly

Initial Comment:
eval() does not bind variables in lambda expressions
correctly:

>>>def f(g): return eval('lambda x: g(x)')
>>>f(lambda y: y * 2)(17)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "<string>", line 1, in <lambda>
NameError: global name 'g' is not defined

The docs say this about eval():

# If both dictionaries are omitted, the expression is
# executed in the environment where eval is called.

and using plain local variables work as expected:

>>>def h(d): return eval('d(10)')
>>>h(lambda y: y * 2)
20

Also, if locals() is presented as the global dict to
eval(), it works:

>>>def f(g): return eval('lambda x: g(x)', locals(),
locals())
>>>f(lambda y: y * 2)(17)
34

but this does not allow the expression to reference
global variables of course.


----------------------------------------------------------------------

Comment By: Terry J. Reedy (tjreedy)
Date: 2005-03-01 00:30

Message:
Logged In: YES 
user_id=593130

I am 99.5% sure that this is 'invalid' (a Resolution category) and 
should be closed.  With the default environment, eval('x') is the 
same as unquoted x.  Variables in Python functions are resolved 
when the function is *called*, not when it is defined.  There is no 
resolution for g in the default globals.  Eval does not change this.  
The NameError is exactly correct.

----------------------------------------------------------------------

You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1153622&group_id=5470