Python Loops & Control Statements

Pradeep

Python Loops & Control Statements

Control statements and loops are basic building blocks for every programming language. In most of the programming languages, control & loop blocks are identified using curly({}) brackets around the control & loop statements. Since Python does not support curly brackets, it is important to have proper indentation to identify the block. Python code will fail without proper indentation.

Control Statements(IF/ELSE)
Loop Statements
1. While Loop
2. For Loop
Loop interruption statements
1. Break
2. Continue

➠ Control Statements(IF/ELSE): If Else statements are called control statements. User can either use round brackets or directly specify the control condition.

IF Statement: Command within 'if' block will only gets executed if the condition specified in the 'if' statement will be True. Below examples will show the usage of if statement.


Example 1: 
a = 2; b = 5
if a < b:
    print(True)
Output: True


Example 2: 
if a < b: print("a is less than b")
Output: a is less than b


Example 3: 
if a > b: print("a is greater than b") #No Output
Output: 


Example 4: 
if 3 in [1,2,3,4]:
   print('3 is present')
Output: 3 is present

IF/ELSE Statement: If the condition in 'if' block is False then only 'else' block will be executed. Below examples will show the usage of if/else statement.


Example 1: 
a = 7; b = 5
if a < b:
    print(True)
else:
    print(False)
Output: False


Example 2: 
if a < b: 
    print("b is greater than a")
else:
    print("a is greater than b")
Output: a is greater than b


Example 3: 
a = 7; b = 10
if a < b: 
    print("b is greater than a")
else:
    print("a is greater than b")
Output: b is greater than a


Example 4: 
if 5 in [1,2,3,4]:
   print('5 is present')
else:
   print('5 is not present')
Output: 5 is not present

IF/ELIF Statement: If the condition in 'if' block is False then only it will check the condition defined for 'elif' and execute the 'elif' block only if condition defined for 'elif' is True. There can be many 'elif' blocks for a single control statement. Below examples will show the usage of if/elif statement.


Example 1: 
a = 7; b = 5
if a < b: 
    print("b is greater than a")
elif( a > b ):
    print("a is greater than b")
Output: a is greater than b


Example 2: 
a = 7; b = 10
if a < b: 
    print("b is greater than a")
elif( a > b ):
    print("a is greater than b")
Output: b is greater than a


Example 3: 
a = 7; b = 5; c=7
if a < c: 
    print("c is greater than a")
elif( a < b ):
    print("b is greater than a")
elif( a==c):
    print("a is equal to c")
Output: a is equal to c


Example 4: 
if 5 in [1,2,3,4]:
   print('5 is present')
elif 4 in [1,2,3,4]:
   print('4 is present')
Output: 4 is present

IF/ELIF/ELSE Statement: Control statements can be created by combination of 'if/elif/else' blocks. Below example will show the usage of if/elif/else statement.


Example 1: 
a = 7; c=7
if a < c: 
    print("c is greater than a")
elif( a > c ):
    print("a is greater than c")
else:
    print("a is equal to c")
Output: a is equal to c

➠ Loop Statements: Loop statements help to iterate over iteratable objects such as List, Set, Tuple or custom iteration which allows code blocks to be executed repeatedly.

For Loop: 'for' loop iterates till the end of index of the objects passed in the for condition which allows code block to be executed repeatedly.


Example 1: 
for x in [0, 1, 2, 3]:
  print(x)
Output: 
0
1
2
3


Example 2: 
for x in [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]:
  if x%2==0:
     print(x)
Output: 
2
4
6
8
10


Example 3: 
for x in range(1,11):
  if x%2==0:
     print(x)
Output: 
2
4
6
8
10

While Loop: 'while' loop will continue to execute code block repeatedly based on a given boolean condition. Boolean condition passed in while loop must be programmatically set to false(when specified condition is met) to exit the loop.
```
Example 1: 
i = 1
while i <= 3:
  print(i)
  i += 1
Output: 
1
2
3


Example 2: 
i = 1
while i <= 9:
  if i%3 == 0:
    print(i)
  i += 1
Output: 
3
6
9
```

➠ Loop interruption statements: There are 2 loop interruption statement(continue & Break) in Python.

Break: Break statement can be used if user has to stop the loop without completing rest of the loop. This statement is mostly used within 'if' block to stop the loop based on particular condition.
```
Example 1: 
i = 1
while i < 6:
  print(i)
  if i == 3:
    break
  i += 1
Output: 
1
2
3 <-- Loop stopped/breaked when i = 3 
```
Continue: Continue statement can be used if user has to ignore the rest of the commands within loop and continue with next iteration of the loop. This statement is also mostly used within 'if' block to continue the loop based on particular condition.
```
Example 1: 
i = 0
while i < 6:
  i += 1 
  if i == 3:
    continue
  print(i)
Output: 
1
2
4 <-- i = 3 is missing because of continue 
5
6  
```

Python Loops & Control Statements

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Python Loops & Control Statements