Python_Loops.pptxpython loopspython loopspython loopspython loopspython loopspython loopspython loops

Python Loops
Python has two primitive loop commands:
• While loops
• for loops

The while Loop:
• With the while loop we can execute a set of statements
as long as a condition is true.
• Example:
i = 1
while i < 6:
print(i)
i += 1
• Output:
1
2
3
4
5

The break Statement(While loop):
• With the break statement we can stop the loop even if
the while condition is true
• Example:
i = 1
while i < 6:
print(i)
if i == 3:
break
i += 1
• Output:
1
2
3

The continue Statement(while loop)
• With the continue statement we can stop the current
iteration, and continue with the next.
• Example:
i = 0
while i < 6:
i += 1
if i == 3:
continue
print(i)
• Output:
1
2
3
4
5
6

The else Statement(while loop)
• With the else statement we can run a block of code once
when the condition no longer is true
• Example:
i = 1
while i < 6:
print(i)
i += 1
else:
print("i is no longer less than 6")
• Output:
1
2
3
4
5
i is no longer less than 6

Python For Loop:
• A for loop is used for iterating over a sequence (that is
either a list, a tuple, a dictionary, a set, or a string).
• This is less like the for keyword in other programming
languages, and works more like an iterator method as
found in other object-orientated programming
languages.
• With the for loop we can execute a set of statements,
once for each item in a list, tuple, set etc.

• Example:
• Print each fruit in a fruit list:
fruits = ["apple", "banana", "cherry"]
for x in fruits:
print(x)
• Output:
Apple
Banana
cherry

Looping Through a String(for loop)
• Even strings are iterable objects, they contain a sequence of
characters.
• Example:
• Loop through the letters in the word "banana“:
for x in "banana":
print(x)
• Output:
b
a
n
a
n
a

The break Statement(for loop)
• With the break statement we can stop the loop before it
has looped through all the items.
• Example:
• Exit the loop when x is “banana”:
for x in fruits:
print(x)
if x == "banana":
break
• Output:
Apple
banana

• Example:
• Exit the loop when x is “banana”,but this time the break comes before the
print:
for x in fruits:
if x == "banana":
break
print(x)
• Output:
Apple

The continue Statement(for loop)
• With the continue statement we can stop the current
iteration of the loop, and continue with the next.
• Example:
• Do not print banana
for x in fruits:
if x == "banana":
continue
print(x)
• Output:
Apple
cherry

The range() Function (for loop)
• To loop through a set of code a specified number of
times, we can use the range() function,
• The range() function returns a sequence of numbers,
starting from 0 by default, and increments by 1 (by
default), and ends at a specified number.
• Example:
for x in range(6):
print(x)
• Output:
0
1
2
3
4
5

• The range() function defaults to 0 as a starting value,
however it is possible to specify the starting value by
adding a parameter: range(2, 6), which means values
from 2 to 6 (but not including 6)
• Example:
for x in range(2, 6):
print(x)
• Output:
2
3
4
5

Else in For Loop
• The else keyword in a for loop specifies a block of code to be executed
when the loop is finished:
• 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!")
• Output:
0
1
2
3
4
5
Finally finished!

Nested Loops
• A nested loop is a loop inside a loop.
• The "inner loop" will be executed one time for each
iteration of the "outer loop"
• Example:
• Print each adjective for every fruit
adj = ["red", "big", "tasty"]
for x in adj:
for y in fruits:
print(x, y)

• Output:
Red apple
Red banana
Red cherry
Big apple
Big banana
Big cherry
Testy apple
Testy banana
Testy cherry

The pass Statement
• For loops can not be empty but if you for some reason have a for loop
with no content, put in the pass statement to avoid getting an error.
• Example:
for x in [0, 1, 2]:
pass
• Output:
# having an empty for loop like this, would raise an
error without the pass statement

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