[ python-Bugs-1649100 ] Arithmetics behaving strange and magic underscore

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Bugs item #1649100, was opened at 2007-01-31 18:36
Message generated for change (Comment added) made by gbrandl
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Category: Parser/Compiler
Group: Python 2.4
>Status: Closed
>Resolution: Invalid
Priority: 5
Private: No
Submitted By: Sascha Peilicke (lastmohican)
Assigned to: Nobody/Anonymous (nobody)
Summary: Arithmetics behaving strange and magic underscore

Initial Comment:
Hello, i just found some strange things going around, could you please tell me if this is desired:

>>> 3 + 4
7
>>> 3 +- 4
-1
>>> 3 +-+ 4
-1
>>> 3 +-+- 4
7
>>> 3 +-+-+ 4
7
>>> 3 +-+-+- 4
-1
>>> 3 +-+-+-+ 4
-1
>>> 3 +-+-+-+- 4
7

This was found in Python 2.4.4c1. And also another one:


>>> _
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
NameError: name '_' is not defined
>>> 3 == 3
True
>>> _
True
>>> 3 
3
>>> _
3


So what the hell is '_' something very strange indeed.

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>Comment By: Georg Brandl (gbrandl)
Date: 2007-01-31 20:22

Message:
Logged In: YES 
user_id=849994
Originator: NO

In your first example, all + and - except the first + are seen as unary
operators and modify the 4.

In your second example: "_" is a convenience variable in the interactive
interpreter and always bound to the
latest expression result. At startup, there is no such result.

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

Comment By: Sascha Peilicke (lastmohican)
Date: 2007-01-31 18:39

Message:
Logged In: YES 
user_id=1465593
Originator: YES

I also found these working on the following:

Python 2.5 (r25:51908, Oct  6 2006, 15:22:41) 
[GCC 4.1.2 20060928 (prerelease) (Ubuntu 4.1.1-13ubuntu4)] on linux2

Seems to be a common 'problem' ?

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You can respond by visiting: 
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