[New-bugs-announce] [issue22511] Assignment Operators behavior within a user-defined function and arguments being passed by reference or value

[Mohammed Mustafa Al-Habshi]

New submission from Mohammed Mustafa Al-Habshi:

hello every one,

I was trying to understand the behavior of passing arguments in a function to differentiate how we can pass argument by value. Though it is a technique matter. However, the behavior of assignment operator += 
when using it with a list is more to toward behavior to the "append" method of the list object, and not like a a normal assignment. 

This causes a confusing when teach python language concepts , especially the behavior of += with numerical data types is list normal assignment and the parameters are then passed by value.

The issue is more related to data type mutability. and I believe assignment operator should be synthetically more compatible with normal assignment.


---- inline code example -----
def pass_(x):
    # x is list type
    print "Within the function"
    print " x was " , x
    #x = x + [50] #  here x is passed by value
    x += [50]    #  here x is passed by reference.
    #x.append(50)   #  here x is passed by reference.
    print " x then is " , x
    return

x = [12,32,12]
pass_(x)
print "\n x out of the function is " , x

----------
messages: 227761
nosy: alhabshi3k
priority: normal
severity: normal
status: open
title: Assignment Operators behavior within a user-defined function and arguments being passed by reference or value
type: behavior
versions: Python 2.7

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue22511>
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