How to use for statement to create a loop in Python
for statement
The for statement performs a block of code for each element in a sequence or other iterable object.
words = ['this', 'is', 'a', 'test', 'from java2s.com']
for word in words:
print word
The code above generates the following result.
or
numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
for number in numbers:
print number
The code above generates the following result.
To loop over the keys of a dictionary, you can use a plain for statement, just as you can with sequences:
d = {'x': 1, 'y': 2, 'z': 3}
for key in d:
print key, 'corresponds to', d[key]
The code above generates the following result.
for loops and sequence unpacking in them:
d = {'x': 1, 'y': 2, 'z': 3}
for key, value in d.items():
print key, 'corresponds to', value
The code above generates the following result.
Parallel Iteration
iterate over two sequences at the same time.
names = ['anne', 'beth', 'george', 'damon']
ages = [12, 45, 32, 102] # ww w .j a v a 2s . c o m
for i in range(len(names)):
print names[i], 'is', ages[i], 'years old'
The code above generates the following result.
else Clauses in Loops
else clause is called if you didn't call break. Let's reuse the example from the preceding section on break:
from math import sqrt
for n in range(99, 81, -1):
root = sqrt(n) # ww w. jav a 2s . c o m
if root == int(root):
print n
break
else:
print "Didn't find it!"
The code above generates the following result.
Nested for loops
items = ["aaa", 111, (4, 5), 2.01] # A set of objects
tests = [(4, 5), 3.14] # Keys to search for
# from w w w . jav a 2 s.co m
for key in tests: # For all keys
for item in items: # For all items
if item == key: # Check for match
print key, "was found"
break
else:
print key, "not found!"
The code above generates the following result.
