See the following code :
choices = ['pizza', 'pasta', 'salad', 'nachos']
print 'Your choices are:'
for index, item in enumerate(choices):
print index+1, item
Output:
Your choices are:
1 pizza
2 pasta
3 salad
4 nachos
None
In the third line, for takes two arguments.
for index, item in enumerate(choices):
But the syntax of for loop is:
array=[...]
for element in array
How does this actually work? Does for loop take in multiple arguments? If yes, how can we use them?
Python lets you unpack sequences on assignment:
>>> foo = ('spam', 'ham')
>>> bar, baz = foo
>>> bar
'spam'
>>> baz
'ham'
The same can be done in a for loop:
list_of_tuples = [('foo', 'bar'), ('spam', 'ham')]
for value1, value2 in list_of_tuples:
print value1, value2
would print
foo bar
spam ham
The enumerate() function produces tuples of two values, the index, and value from the sequence passed in as an argument:
>>> seasons = ['Spring', 'Summer', 'Fall', 'Winter']
>>> list(enumerate(seasons))
[(0, 'Spring'), (1, 'Summer'), (2, 'Fall'), (3, 'Winter')]
Actually, it takes one argument, of type tuple, which is then unpacked.
The syntax is similar to the following:
a, b = b, a
which is a nice way of writing a "swap" of the two variables.
However, think of it as
(a,b) = (b,a)
Then you have a "single tuple" assignment, combined with tuple unpacking.
It's tuple unpacking. In an assignment, you can put a tuple of variables on the left side and if the right side has exactly that amount of elements, they get assigned like that:
a, b = (3, 4) # Now a is 3 and b is 4
You can do that in for loops as well
for a, b in [(3, 4), (5, 6)]:
print(a)
will print 3 and then 5.
Since enumerate yields tuples of (index, element), the for loop in your element works.
forloop is actuallyfor things in otherThings, notfor elem in array: docs.python.org/2/reference/compound_stmts.html#for