7-conditions.py

# Tutorial: http://www.learnpython.org/en/Conditions

# Conditions
# Python uses boolean variables to evaluate conditions. The boolean values True and False are returned when an expression is compared or evaluated. For example:

x = 2
print(x == 2) # prints out True
print(x == 3) # prints out False
print(x < 3) # prints out True

# Notice that variable assignment is done using a single equals operator "=", whereas comparison between two variables is done using the double equals operator "==". The "not equals" operator is marked as "!=".

# Boolean operators
# The "and" and "or" boolean operators allow building complex boolean expressions, for example:

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
# The "in" operator could be used to check if a specified object exists within an iterable object container, such as a list:

name = "John"
if name in ["John", "Rick"]:
    print("Your name is either John or Rick.")
    
# Python uses indentation to define code blocks, instead of brackets. The standard Python indentation is 4 spaces, although tabs and any other space size will work, as long as it is consistent. Notice that code blocks do not need any termination.
# Here is an example for using Python's "if" statement using code blocks:

# if <statement true="" is="">:
    # <do something="">
    # ....
    # ....
# elif <another true="" is="" statement="">: # else if
    # <do something="" else="">
    # ....
    # ....
# else:
    # <do thing="" another="">
    # ....
    # ....
# </do></do></another></do></statement>

# For example:

x = 2
if x == 2:
    print("x equals two!")
else:
    print("x does not equal to two.")
    
# A statement is evaulated as true if one of the following is correct: 1. The "True" boolean variable is given, or calculated using an expression, such as an arithmetic comparison. 2. An object which is not considered "empty" is passed.
# Here are some examples for objects which are considered as empty: 1. An empty string: "" 2. An empty list: [] 3. The number zero: 0 4. 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. For example:

x = [1,2,3]
y = [1,2,3]
print(x == y) # Prints out True
print(x is y) # Prints out False

# The "not" operator
# Using "not" before a boolean expression inverts it:

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 = 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")