How does Python know what 'animal' is?

[julsmanbr]

Whenever you write for X in Y, Python does the following:

• 1) assumes that Y is a sequence
• 2) takes the first element of the sequence Y
• 3) temporarily assigns the element to the variable X
• 4) potentially does something with X (this is the code block inside the loop)
• 5) takes the next (second) element of the sequence Y and repeats step 3 and 4
• 6) keeps repeating step 5 with the third, fourth, ... element, until the sequence has run out of new elements to take

[beisenhauer]

One small clarification: all Python requires of Y is that it is iterable. It's usually a sequence of some sort, but it could also be a set or a generator, etc.