Python If

The if statement¶ The if statement is used for conditional execution: ifstmt::= 'if'. The ‘or’ in Python is a logical operator that evaluates as True if any of the operands is True, unlike the ‘and’ operator where all operands have to be True. An OR example ‘and’ ‘or’ example. For example, if we check x 10 and y 20 in the if condition. If either of the expression is True, the code inside the if statement will execute.

  1. Python If Statement
  2. Python If Loop
  3. Python If
  4. Python If Or
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Python follows a convention known as the off-side rule, a term coined by British computer scientist Peter J. (The term is taken from the offside law in association football.) Languages that adhere to the off-side rule define blocks by indentation. Python is one of a. Typically, conditional statements in Python begin with if, and without it, they're hardly logical at all. However, conditions are a set of programmer-defined rules that check if a particular event is true or false. In essence, they check the validity of an event. An if statement in Python generally takes this format.

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An else statement can be combined with an if statement. An else statement contains a block of code that executes if the conditional expression in the if statement resolves to 0 or a FALSE value.

The else statement is an optional statement and there could be at the most only one else statement following if.

Syntax

The syntax of the if...else statement is −

Flow Diagram

Example

Output

In the above example, discount is calculated on the input amount. Rate of discount is 5%, if the amount is less than 1000, and 10% if it is above 10000. When the above code is executed, it produces the following result −

The elif Statement

The elif statement allows you to check multiple expressions for TRUE and execute a block of code as soon as one of the conditions evaluates to TRUE.

Similar to the else, the elif statement is optional. However, unlike else, for which there can be at the most one statement, there can be an arbitrary number of elif statements following an if.

Python If Statement

syntax

Core Python does not provide switch or case statements as in other languages, but we can use if..elif...statements to simulate switch case as follows −

Example

When the above code is executed, it produces the following result −

Python Conditions and If statements

Python supports the usual logical conditions from mathematics:

  • Equals: a b
  • Not Equals: a != b
  • Less than: a < b
  • Less than or equal to: a <= b
  • Greater than: a > b
  • Greater than or equal to: a >= b

These conditions can be used in several ways, most commonly in 'if statements' and loops.

An 'if statement' is written by using the if keyword.

Example

If statement:

a = 33
b = 200
if b > a:
print('b is greater than a')
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In this example we use two variables, a and b, which are used as part of the if statement to test whether b is greater than a. As a is 33, and b is 200, we know that 200 is greater than 33, and so we print to screen that 'b is greater than a'.

Indentation

Python relies on indentation (whitespace at the beginning of a line) to define scope in the code. Other programming languages often use curly-brackets for this purpose.

Example

If statement, without indentation (will raise an error):

a = 33
b = 200
if b > a:
print('b is greater than a') # you will get an error
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Elif

The elif keyword is pythons way of saying 'if the previous conditions were not true, then try this condition'.

Example

a = 33
b = 33
if b > a:
print('b is greater than a')
elif a b:
print('a and b are equal')
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In this example a is equal to b, so the first condition is not true, but the elif condition is true, so we print to screen that 'a and b are equal'.

Else

Python If

The else keyword catches anything which isn't caught by the preceding conditions.

Example

a = 200
b = 33
if b > a:
print('b is greater than a')
elif a b:
print('a and b are equal')
else:
print('a is greater than b')
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In this example a is greater than b, so the first condition is not true, also the elif condition is not true, so we go to the else condition and print to screen that 'a is greater than b'.

You can also have an else without the elif:

Example

a = 200
b = 33
if b > a:
print('b is greater than a')
else:
print('b is not greater than a')
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Short Hand If

If you have only one statement to execute, you can put it on the same line as the if statement.

Python If Loop

Example

One line if statement:

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Short Hand If ... Else

If you have only one statement to execute, one for if, and one for else, you can put it all on the same line:

Example

One line if else statement:

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This technique is known as Ternary Operators, or Conditional Expressions.

You can also have multiple else statements on the same line:

Example

One line if else statement, with 3 conditions:

Python
a = 330
b = 330
print('A') if a > b else print('=') if a b else print('B')

Python If

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And

The and keyword is a logical operator, and is used to combine conditional statements:

Example

Test if a is greater than b, AND if c is greater than a:

a = 200
b = 33
c = 500
if a > b and c > a:
print('Both conditions are True')
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Or

The or keyword is a logical operator, and is used to combine conditional statements:

Example

Test if a is greater than b, OR if a is greater than c:

Python If
a = 200
b = 33
c = 500
if a > b or a > c:
print('At least one of the conditions is True')
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Nested If

You can have if statements inside if statements, this is called nestedif statements.

Example

x = 41
if x > 10:
print('Above ten,')
if x > 20:
print('and also above 20!')
else:
print('but not above 20.')
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The pass Statement

if statements cannot be empty, but if you for some reason have an if statement with no content, put in the pass statement to avoid getting an error.

Python If Or

Example

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