PythonIf ... Else
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 theif keyword.
In this example we use two variables,a andb,which are used as part of the if statement to test whetherb is greater thana.Asa is33, andb is200,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):
b = 200
if b > a:
print("b is greater than a")# you will get an error
Elif
Theelif keyword is Python's way of saying "if the previous conditions were not true, then try this condition".
Example
b = 33
if b > a:
print("b is greater than a")
elif a == b:
print("a and b are equal")
In this examplea is equal tob, so the first condition is not true, but theelif condition is true, so we print to screen that "a and b are equal".
Else
Theelse keyword catches anything which isn't caught by the preceding conditions.
Example
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")
In this examplea is greater thanb,so the first condition is not true, also theelif condition is not true,so we go to theelse condition and print to screen that "a is greater than b".
You can also have anelse without theelif:
Example
b = 33
if b > a:
print("b is greater than a")
else:
print("b is not greater than a")
Short Hand If
If you have only one statement to execute, you can put it on the same line as the if statement.
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:
This technique is known asTernary Operators, orConditional Expressions.
You can also have multiple else statements on the same line:
Example
One line if else statement, with 3 conditions:
b = 330
print("A") if a > b else print("=") if a == b else print("B")
And
Theand keyword is a logical operator, and is used to combine conditional statements:
Example
Test ifa is greater thanb, AND ifc is greater thana:
b = 33
c = 500
if a > b and c > a:
print("Both conditions are True")
Or
Theor keyword is a logical operator, and is used to combine conditional statements:
Example
Test ifa is greater thanb, OR ifa is greater thanc:
b = 33
c = 500
if a > b or a > c:
print("At least one of the conditions is True")
Not
Thenot keyword is a logical operator, and is used to reverse the result of the conditional statement:
Example
Test ifa is NOT greater thanb:
b = 200
if not a > b:
print("a is NOT greater than b")
Nested If
You can haveif statements insideif statements, this is callednestedif statements.
Example
if x > 10:
print("Above ten,")
if x > 20:
print("and also above 20!")
else:
print("but not above 20.")
The pass Statement
if statements cannot be empty, but if you for some reason have anif statement with no content, put in thepass statement to avoid getting an error.
