For loops¶
A for loop executes commands once for each value in a collection.¶
Doing calculations on the values in a list one by one is as painful as working with
pressure_001
,pressure_002
, etc.A for loop tells Python to execute some statements once for each value in a list, a character string, or some other collection.
“for each thing in this group, do these operations”
for number in [2, 3, 5]:
print(number)
This
for
loop is equivalent to:
print(2)
print(3)
print(5)
And the
for
loop’s output is:
A for
loop is made up of a collection, a loop variable, and a body.¶
for number in [2, 3, 5]:
print(number)
A for
loop is made up of a collection, a loop variable, and a body.¶
The collection,
[2, 3, 5]
, is what the loop is being run on.The body,
print(number)
, specifies what to do for each value in the collection.The loop variable,
number
, is what changes for each iteration of the loop.The “current thing”.
The first line of the for
loop must end with a colon, and the body must be indented.¶
The colon at the end of the first line signals the start of a block of statements.
Python uses indentation rather than
{}
orbegin
/end
to show nesting.Any consistent indentation is legal, but almost everyone uses four spaces.
for number in [2, 3, 5]:
print(number)
Indentation is always meaningful in Python.
firstName = "Jon"
lastName = "Smith"
This error can be fixed by removing the extra spaces at the beginning of the second line.
Loop variables can be called anything.¶
As with all variables, loop variables are:
Created on demand.
Meaningless: their names can be anything at all.
for anything in range(5):
print(anything)