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Python For Loops
Python For Loops
A for loop is used for repetition in sequence (i.e. list, tuple, dictionary, set, or character unit).
This is similar to the for keyword in some editing languages, and serves as a repetition method as found in other object-focused editing languages.
With a for loop we can make a set of statements, as well as each item in the list, tuple, set etc.
Example
Print each fruit in a fruit list:
fruits = ["apple", "banana", "cherry"]
for
x in fruits:
print(x)
The for loop does not require variable indexing to be pre-configured.
Looping Through a String
Even cables are controllable, consisting of a series of letters:
Example
Loop through the letters in the word "banana":
for x in "banana":
print(x)
The break Statement
With a break statement we can stop the loop before it goes into all things:
Example
Exit the loop when x is "banana":
fruits = ["apple", "banana", "cherry"]
for x in fruits:
print(x)
if x ==
"banana":
break
Example
Exit the loop when x is "banana", but this time the break comes before the print:
fruits = ["apple", "banana", "cherry"]
for x in fruits:
if x ==
"banana":
break
print(x)
The continue Statement
With an continue statement we can stop the current duplicate of the loop, and proceed to the following:
Example
Do not print banana:
fruits = ["apple", "banana", "cherry"]
for x in fruits:
if x ==
"banana":
continue
print(x)
The range() Function
To connect to a set of code a certain number of times, we can use the range() function,
The range() function returns the sequence of numbers, from 0 by default, to increments by 1 (by default), and ends at a certain number.
Example
Using the range() function:
for x in range(6):
print(x)
Note that the range(6) is not a value of 0 to 6, but a value of 0 to 5.
range() function varies by 0 as the first value, however it is possible to specify the first value by adding a parameter: range(2, 6), meaning values from 2 to 6 (but excluding 6):
Example
Using the start parameter:
for x in range(2, 6):
print(x)
The range() function is automatically adjusted to increase the sequence by 1, however it is possible to specify an additional value by adding a third parameter: range(2, 30, 3):
Example
Increment the sequence with 3 (default is 1):
for x in range(2, 30, 3):
print(x)
Else in For Loop
else keyword in the for loop specifies the code block to be used when the loop is complete:
Example
Print all numbers from 0 to 5, and print a message when the loop has ended:
for x in range(6):
print(x)
else:
print("Finally finished!")
Note: Else block will NOT be used if the loop is stopped by a break statement.
Example
Break the loop when x is 3, and see what happens with the else block:
for x in range(6):
if x == 3: break
print(x)
else:
print("Finally finished!")
Nested Loops
A loop with a nest is a loop inside a loop.
"Internal loop" will be used simultaneously for each duplicate of "external loop":
Example
Print each adjective for every fruit:
adj = ["red", "big", "tasty"]
fruits = ["apple", "banana", "cherry"]
for x in adj:
for y in fruits:
print(x, y)
The pass Statement
because the for loops cannot be empty, but if for some reason you have a for loop with no content, enter a pass statement to avoid finding error.
Example
Print each adjective for every fruit:
for x in [0, 1, 2]:
pass