How does Python for loop work?

Question

I am used to the C++ way of for loops, but the Python loops have left me confused.

for party in feed.entry:
    print party.location.address.text

Here party in feed.entry. What does it signify and how does it actually work?

Answer 1

feed.entry is something that allows iteration, and contains objects of some type. This is roughly similar to c++:

for (feed::iterator party = feed.entry.begin(); party != feed.entry.end(); ++party) {
   cout << (*party).location.address.text;
}

Answer 2

feed.entry is property of feed and it's value is (if it's not, this code will fail) object implementing iteration protocol (array, for example) and has iter method, which returns iterator object

Iterator has next() method, returning next element or raising exception, so python for loop is actually:

iterator = feed.entry.__iter__()
while True:
    try:
        party = iterator.next()
    except StopIteration:
        # StopIteration exception is raised after last element
        break

    # loop code
    print party.location.address.text

Answer 3

party simply iterates over the list feed.entry

Take a look at Dive into Python explainations.

Answer 4

In Python, for bucles aren't like the C/C++ ones, they're most like PHP's foreach. What you do isn't iterate like in a while with "(initialization; condition; increment)", it simply iterates over each element in a list (strings are ITERABLE like lists).

For example:

for number in range(5):
    print number

will output

0
1
2
3
4

Answer 5

To add my 0.05$ to the previous answers you might also want to take a look at the enumerate builtin function

for i, season in enumerate(['Spring', 'Summer', 'Fall', 'Winter']):
    print i, season

0 Spring
1 Summer
2 Fall
3 Winter

Answer 6

Python's for loop works with iterators, which must implement the iterator protocol. For more details see:

• Build a Basic Python Iterator