Python If ... 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 the if keyword.
a = 33
b = 200
if b > a:
print("b is greater than a")
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.
a = 33
b = 200
if b > a:
print("b is greater than a")
# you will get an error
Elif
The elif keyword is pythons 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")
Short Hand If
If you have only one statement to execute, you can put it on the same line as the if statement.
if a > b: print("a is greater than b")
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:
a = 2
b = 330
print("A") if a > b else print("B")
And
The and keyword is a logical operator, and is used to combine conditional statements:
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:
a = 200
b = 33
c = 500
if a > b or a > c:
print("At least one of the conditions is True")
Nested 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.")
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.
a = 33
b = 200
if b > a:
pass
