Conditional Statements

• Think of conditional statement as a test
• Returns True or False

Python if syntax

if expression_1:
elif expression_2:

• Python evaluates the if and elif statements starting with the first and proceeding to the last
• If any of expressions evaluate to True, it runs the block of statements associated with that if/elif clause and then skips the rest of the clauses and continues with the next statement after the if-block

#!/usr/bin/bash/env python3

my_name = "Dave"
my_age = 30

# Tests --these are basic logic
# What would the REPL say after you typed these in?

    # Equality
    my_name == 'Dave'
    # Inequality
    my_name != 'Steve'
    # Greater than / Less than
    my_age > 60
    my_age < 60
        # GTE, LTE
        my_age >= 60
        my_age <= 60
# Combinations
age > 16 and age < 100
16 < age < 100              # better

True and False
True and True
True or False               # the 2nd one 'False' never evaluated
False or True               # evaluates both

# Booleans -- the thing we're actually dealing with
0 == False
1 == True

is_authenticated = True
is_admin = False

If Elif and Else

#!/usr/bin/env python3

# Simple Structure
# if conditional_statement:
#    statement()
# Example
command = "destroy datacores"
if command == "destroy datacores":
    print("Destroying all datacores")

# Optional Else
if command == "hello" and 8 > 1:
    print("This executes only if the first conditinal was False")
# Optional Elif (between original conditional test and 'else' keyword)
command = input("How would you like to proceed?\n").lower()

if command == "destroy datacores":
    print("Destroying all datacores")

elif command == "shut down":
    print("Shutting the system down")

elif command == "premabork the frambulator":
    print("Are you sure? You will not be able to unbork this later..")

# None of the others evaluated to True...
    print("Command not understood")

Only the First Elif Runs

• Some language will execute both elif per example below but not python

# The first one to evaluate to True 'wins'
if 3 !=3:
elif 8 == 8:
    print('First True elif found...')
elif 8 > 4:
    print('Second True elif found...')
# Output
# First True elif found...

Nested If Elif and Else

print("This happens before the 'if' block.")

user_is_admin = True

# What conditionals allow you to do
if user_is_admin:
    print("Access Granted.")
    command = input("How would you like to proceed? ")
    command = command.lower()
    if command = "destroy datacores":
        print("Destroying all datacores")
    elif command == "exit":
        print("You don't have the guts, do you?")
    print("Access Denied.")
print("This happens after the 'if' block.")