If ... Else in Python
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.
If statement:
a = 33
b = 200
if b > a:
print("b is greater than a")
elif:
Example: The elif keyword is Python's way of saying "if the previous conditions were not true, then try this condition".
a = 33
b = 33
if b > a:
print("b is greater than a")
elif a == b:
print("a and b are equal")
else:
The else keyword catches anything which isn't caught by the preceding conditions.
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")
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:
a = 200
b = 33
if b > a:
print("b is greater than a")
else:
print("b is not greater than a")
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")
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:
a = 200
b = 33
c = 500
if a > b or a > c:
print("At least one of the conditions is True")
Not
The not keyword is a logical operator, and is used to reverse the result of the conditional statement:
Example: Test if a is NOT greater than b:
a = 33
b = 200
if not a > b:
print("a is NOT greater than b")
Nest if
You can have if statements inside if statements, this is called nested if statements.
x = 41
if x > 10:
print("Above ten,")
if x > 20:
print("and also above 20!")
else:
print("but not above 20.")