Learn to control the flow of a Python program using
if...elseif statements. These statements are called conditional statements and help in writing boolean conditions that generally compare two variables or expressions.
a = 0 if a > 0: print("a is greater than 0") elif a < 0: print("a is less than 0") else: print("a is 0")
1. Using if
An “if statement” is written by using the
a = 10 b = 20 if b > a: print("b is greater than a") #Prints this message
Python uses indentation to define the scope in the code. (Similar to curly brackets in Java). So be mindful of indentation while writing if else statements in Python.
1.2. Combining Multiple Expressions with Logical Operators
We can combine multiple expressions in the if statement using logical operators. Python provides two logical operators:
and: Logical AND
or: Logical OR
The following condition tests that b and c, both, are greater than a.
a = 10 b = 20 c = 30 if b > a and c > a: print("b and c are greater than a") #Prints this message
1.3. Shorthand if
Whenever there is only a single statement to be executed inside the if block then shorthand if statement can be used. The statement can be put on the same line as the if statement.
if b > a: print("b is greater than a")
2. Using if … else
The if statement is executed only if a certain condition is True. If the condition is False, then
else statement is executed if provided in the program.
a = 100 b = 20 if b > a: print("b is greater than a") else: print("b is smaller than a") #Prints this message
We can write the shorthand if-else statement similar to the shorthand if statement we saw in the first section. Its syntax is:
statement_when_True if condition else statement_when_False
Let us rewrite the previous example in shorthand if-else statement.
a = 100 b = 20 print("b is greater than a") if (b > a) else print("b is smaller than a") #Prints 'b is smaller than a'
3. Using elif
elif statement is short form of
else if statements in other programming languages such as Java. A
Elif statement containing a conditional expression will be executed if its previous conditional expression is evaluated as False.
In this example, x is greater than y so the
if statement will be False. So, the program will execute the
elif statement which is True.
x = 100 y = 200 z = 300 if y < x: print('y is less than x') elif y < z: print('y is less than z') #Prints this message
4. Nested if .. else
We can have
if statements inside another
if statements, this is called nested
if statements. We can compile these statements up to any level.
a = 20 if a > 10: print("a is greater than 10") #Prints this message if a < 20: print("a is less than 20") else: print("a is equal to 20") #Prints this message
5. Empty if
A Python program cannot have an empty
if statement. If for any reason, you must provide an empty
if statement then use the
x = 100 y = 200 if x < y: pass
Happy Learning !!
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