Iterating Over A List

The for statement lets you iterate over a list. It selects items from the list one by one, starting with the first and continuing until it reaches the end of the list.

Here is an example

for i in [1, 2, 3]:

    print i

Each time the loop executes, the variable "i" takes on the value of the next item in the list.

You might be used to writing code like this

x = [1, 2, 3]

for i in range(len(x)):

    print x[i]

Although this works, it introduces a needless counting variable and two unnecessary function calls (range and len). The first form shown above is easier to write and more efficient.

Iterating over a part of a list

What if you just want to iterate over a part of a list? You should take a slice and iterate over the slice.

x = [1, 2, 3, 4, 5]

# iterate over the first 3 values

for i in x[:3]:

    print i

Again, this is simpler than using the range function to generate a series of index values

x = [1, 2, 3, 4, 5]

# iterate over indexes 0..2

for i in range(0,3):

    print x[i]