Question

Can anyone explain how x is taking integer values. We are directly using x in for loop “for x in a”
How is the compiler going to recognize it that x represents the strings inside the list?

>>> # Measure some strings:
... a = ['cat', 'window', 'defenestrate']
>>> for x in a:
... print x, len(x)
...
cat 3
window 6
defenestrate 12

Answer 1

for works differently in Python than it works in languages like C. Instead of counting up/down a numerical value and checking an end condition as you usually would in C:

for (i=0; i<=max; i++) do_something();

it iterates over all the elements in the container (whose name is referenced after the in):

for item in iterable:
    do_something(item)

Its precise behavior depends on the type of container (iterable) used; in a list or tuple, it will start at the first element, then move through the list/tuple one item at a time until the final element has been reached. Each of the elements will be then referenced by a name (item in this example) so that it can be operated on in the body of the loop.

In a dictionary, for would iterate through the dictionary’s keys (in an unspecified order), so item would contain a key of the dictionary.

In a string, it iterates through the letters of the string, one by one. Etc.