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Python - Conditions

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• Python - Conditions
  • IF Statement
  • Conditional expressions
  • Equivalent Expression

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IF Statement

• 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.

• Logical Condition

  • 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

• elif is Python’s way of saying “if the previous conditions were not true, then try this condition”.

• else: catches anything which isn’t caught by the preceding conditions.

• pass: avoid getting an error due to if statement with no content

print("\n--------If Statement--------\n")
a = 33
b = 200
if b > a:
    # print("b is greater than a") # IndentationError: expected an indented block
    print("b is greater than a")


print("\n--------Elif Statement--------\n")
a = 33
b = 33
if b > a:
    print("b is greater than a")
elif a == b:
    print("a and b are equal")


print("\n--------Else Statement--------\n")
a = 200
b = 33
if b > a:
  print("b is greater than a")
else:
  print("b is not greater than a")


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")


print("\n--------Pass Statement--------\n")
a = 33
b = 200

if b > a:
  pass

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Conditional expressions

• Conditional expressions (sometimes called a ternary operator)

  • allows testing a condition in a single line.

• Syntax:

  • [on_true] if [expression] else [on_false]

print("\n--------Conditional expressions--------\n")
a, b = 10, 20
min = a if a < b else b
max = a if a > b else b
print('min: ', min)
print('max: ', max)


# 等价
a, b = 10, 20
if a < b:
    print(b, "is greater")
elif a > b:
    print(b, "is greater")
else:
    print("Equal")

a, b = 20, 20
print(b, "is greater") if a < b else print(
    a, "is greater") if a > b else print("Euqal")


# Define the data to be evaluated
data = [3, 5, 2, 8, 4]
# Use a for loop to evaluate each element in the data
for num in data:
    # Use the ternary operator to determine if the number is even or odd
    result = 'even' if num % 2 == 0 else 'odd'
    # Optionally, print the result of the ternary operator for each element
    print(f'The number {num} is {result}.')

# The number 3 is odd.
# The number 5 is odd.
# The number 2 is even.
# The number 8 is even.
# The number 4 is even.ss

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Equivalent Expression

# Ternary operator
a, b = 10, 20
min = a if a < b else b
print(min)


# Use tuple for selecting an item
# (if_test_false,if_test_true)[test]
# if [a<b] is true it return 1, so element with 1 index will print
# else if [a<b] is false it return 0, so element with 0 index will
a, b = 10, 20
min = (b, a)[a < b]
print(min)


# Use Dictionary for selecting an item
# if [a < b] is true then value of True key will print
# else if [a<b] is false then value of False key will print
a, b = 10, 20
min = {True: a, False: b}[a < b]
print(min)


# lambda is more efficient than above two methods
# because in lambda  we are assure that
# only one expression will be evaluated unlike in
# tuple and Dictionary
a, b = 10, 20
print((lambda: b, lambda: a)[a < b]())

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