Please explain this python behavior

Question

class SomeClass(object):
    def __init__(self, key_text_pairs = None):
        .....
        for key, text in key_text_pairs:
            ......
            ......

x = SomeClass([(1, "abc",), (2, "fff",)])

The value of key_text_pairs inside the init is None even if I pass a list as in the above statement. Why is it so??

I want to write a generic init which can take all iterator objects...

Thanks

Edit: oops.. I wanted to pass key value pair in the form of tuple... I was just trying to create a toy example.. I am still seeing the same behavior

Answer 1

First of all, when you say for key, text in key_text_pairs, you are implying that the list has tuples. I tested your code exactly the way it is and that's what happened.

Change x = SomeClass([1, 2, 3]) to x = SomeClass([(1, 1.0), (2, 2.0), (3, 3.0)]) and see if that helps

Cheers

Answer 2

So just looking at that code, is what you posted exactly what you want? Specifically, if you're passing in a list that looks like:

[1, 2, 3]

Then I don't think you want to try to extract it like this:

for key, text in key_text_pairs

You can extract a list of individual integers into a pair of values like key/text.

If I run that code as you posted it, I get a stack trace:

Traceback (most recent call last):
  File "test.py", line 6, in <module>
    x = SomeClass([1, 2, 3])
  File "test.py", line 3, in __init__
    for key, text in key_text_pairs:
TypeError: 'int' object is not iterable

You either need to do something like this (extract one value at a time):

class SomeClass(object):
    def __init__(self, key_text_pairs = None):
        for key in key_text_pairs:
            ....

x = SomeClass([1, 2, 3])

Or your original list needs to change to be holding pairs of values if you're going to keep that code the same:

x = SomeClass([('a',1),('b',2),('c',3)])

Answer 3

Could you post a traceback?

This is what I get when I run the code:

In [1]: class SomeClass(object):
   ...:     def __init__(self, key_text_pairs = None):
   ...:         for key, text in key_text_pairs:
   ...:             print "key:", key, "text", text
   ...:             
   ...:             

In [2]: x = SomeClass([1,2,3])
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)

/home/ryan/<ipython console> in <module>()

/home/ryan/<ipython console> in __init__(self, key_text_pairs)

TypeError: 'int' object is not iterable

In [3]: x = SomeClass(zip('abc', [1,2,3]))
key: a text 1
key: b text 2
key: c text 3