Tuple unpacking in for loops

Question

I stumbled across the following code:

for i,a in enumerate(attributes):
   labels.append(Label(root, text = a, justify = LEFT).grid(sticky = W))
   e = Entry         


        

Answer 1

You could google on "tuple unpacking". This can be used in various places in Python. The simplest is in assignment

>>> x = (1,2)
>>> a, b = x
>>> a
1
>>> b
2

In a for loop it works similarly. If each element of the iterable is a tuple, then you can specify two variables and each element in the loop will be unpacked to the two.

>>> x = [(1,2), (3,4), (5,6)]
>>> for item in x:
...     print "A tuple", item
A tuple (1, 2)
A tuple (3, 4)
A tuple (5, 6)
>>> for a, b in x:
...     print "First", a, "then", b
First 1 then 2
First 3 then 4
First 5 then 6

The enumerate function creates an iterable of tuples, so it can be used this way.