Python Statements(Control Flow)

In python, colon and indentation is used in control flow syntax. Indentation is very crucial in python. Let’s have look on various python statements:

if statements

Syntax of if statement:

if condition:   
    #code        #indentation is used here

Syntax of if/else statement:

if condition:   
    #code        #indentation is used here
else:
    #code        #indentation is used here

If you are using multiple conditions then use elif:

if condition:   
    #code           #indentation is used here
elif condition_1:   
    #code           #indentation is used here
else:
    #code           #indentation is used here

Let’s see an example:

>>> x = 5
>>> if x < 0:
...     print('X is negative')
... elif x == 0:
...     print('X is Zero')
... else:
...     print('X is positive')
...
X is positive

for Statements

Using for statement, you can iterate over the object. It goes through items that are in a sequence or any other iterable item.

Syntax of for loop:

#numbers.py file
numbers = [1,2,3,4,5,6]   #looping over a list
for n in numbers:
    print(n)
Output:
1
2
3
4
5
6
A) How to print even numbers??
-> Add if statement inside a for loop as follows:
numbers=[1,2,3,4,5,6]  # numbers.py file
for n in numbers:
    if n%2 ==0:    #checking whether number is divisible by 2 or not
        print(n)
Output:
2
4
6

looping over a string:

name="ANKIT"
for n in name:
    print(n)
Output:
A
N
K
I
T

looping over Dictionary:

dict={'john':1,'steve':2,'ricky':3} #dict.py file
for key in dict:
    print(key)
Output:
john
steve
ricky

This is printing only keys. Then how to produce values or key and value together?

Let’s see:

#print values
dict={'john':1,'steve':2,'ricky':3} #dict.py file
for value in dict.values():
    print(value)
Output:
2
1
3
#print key and value
dict={'john':1,'steve':2,'ricky':3} 
for key,value in dict.items():
    print(key,value)
Output:
john 1
steve 2
ricky 3

Note: Since, Dictionaries are unordered, keys and values come in arbitrary order.

while statements

while loop will continue to execute the code till the condition is true.

Syntax:

while condition:     
    code text
else:     
    code text

Let’s see an example:

x=0
while x < 10:
    print(x)
    x+=1
Output:
1
2
3
4
5
6
7
8
9

break and continue statements

break: Breaks out of the current closest enclosing loop.

continue: Goes to the top of the closest enclosing loop.

pass: Does nothing. It can be used when a statement is required syntactically but the program requires no action

break and continue can appear anywhere in the loop body.

for example: in following example, if x equals 5 then execution of while loop will be stopped.

x=0
while x < 10:
    print(x)
    if x==5:
        break
    x+=1
Output:
1
2
3
4
5
# continue statement example
x=0
while x < 10:
    x+=1
    print(x)
    if x==5:
        print("Value is 5")
    else:
        continue           #go to the top of the loop
Output:
1
2
3
4
5
value is 5
6
7
8
9
10

That’s it! We have covered the basics for Python statements.

Happy Coding!