Python Conditions
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.
x = 2
print(x == 2) # prints out True
print(x == 3) # prints out False
print(x < 3) # prints out True
Boolean operators
The "and" and "or" boolean operators allow building complex boolean expressions.
name = "John"
age = 23
if name == "John" and age == 23:
print("Your name is John, and you are also 23 years old.")
if name == "John" or name == "Rick":
print("Your name is either John or Rick.")
The "in" operator could be used to check if a specified object exists within an iterable object container, such as a list:
name = "John"
age = 23
if name in ["John", "Rick"]:
print("Your name is either John or Rick.")
A statement is evaluated as true if one of the following is correct:
- The "True" boolean variable is given, or calculated using an expression, such as an arithmetic comparison.
- An object which is not considered "empty" is passed.
Here are some examples for objects which are considered as empty:
- An empty string:
""
- An empty list:
[]
- The number zero:
0
- The false boolean variable:
False
The 'is' operator
Unlike the double equals operator "==", the "is" operator does not match the values of the variables, but the instances themselves.
x = [1,2,3]
y = [1,2,3]
print(x == y)
print(x is y)
The "not" operator
print(not False) # Prints out True
print((not False) == (False)) # Prints out False
Exercise
Change the variables in the first section, so that each if statement resolves as True.
# change this code
number = 10
second_number = 10
first_array = []
second_array = [1,2,3]
if number > 15:
print("1")
if first_array:
print("2")
if len(second_array) == 2:
print("3")
if len(first_array) + len(second_array) == 5:
print("4")
if first_array and first_array[0] == 1:
print("5")
if not second_number:
print("6")
# change this code
number = 16
second_number = 0
first_array = [1,2,3]
second_array = [1,2]
if number > 15:
print("1")
if first_array:
print("2")
if len(second_array) == 2:
print("3")
if len(first_array) + len(second_array) == 5:
print("4")
if first_array and first_array[0] == 1:
print("5")
if not second_number:
print("6")
test_output_contains("1")
test_output_contains("2")
test_output_contains("3")
test_output_contains("4")
test_output_contains("5")
test_output_contains("6")
success_msg("Excellent!")