Conditionals in Python

Similar to for-loops in Python, conditionals provide a mechanism to control the flow of execution of a program in many programming languages. In Python, the if-statement will run a section of code if and only if the conditional provided is true.

Many people consider 7 to be a lucky number. The Python code below uses an if statement to print out a message if Python randomly choose a lucky number:

num = random.randint(1, 10)
if num == 7:
  print("Today")
  print("is")
  print("Your Lucky Day!")
print(f"Number: {num}")

There are a few features to notice:

• The line of code begins with an if, then followed by a conditional, and ends with a colon (:).
• The block of code following the for statement is indented. This indentation defines the block of code that will run ONLY if the conditional is true.
• The code after the if-statement, back at the original indentation, will only run after the for-loop finishes running.

Notice the two different outputs of the same code based on the randomly generated value:

num = random.randint(1, 10)
if num == 7:
  print("Today")
  print("is")
  print("Your Lucky Day!")
print(f"Number: {num}")

Number: 3

Today
is
Your Lucky Day!
Number: 7

Conditional Syntax

In Python, the conditional component of an if-statement is nearly identical to the conditionals you have used with Pandas except that you are no longer working within the context of a DataFrame.

• You will use if statements to compare the values of individual variables in Python (ex: values as part of a simulation) instead of values in a DataFrame.
• You can still use the six logical operators, ==, >, >=, < <=, and !.
• You can still combined multiple conditionals, except you must use and and or (instead of & and |).

else Statement

Often you may want to run different code when a conditional is true and false. To run code when the conditional is false, an else statement is used. Since else is a control flow statement, it needs a colon (:) at the end and nothing else!

flip = random.choice(["heads", "tails"])
if flip == "heads":
  print("Your coin flipped heads!")
else:
  print("Your coin flipped tails!")

Your coin flipped heads!

Your coin flipped tails!

Application of if-statements: Conditional Data on Simulation

One of the most useful applications of conditionals is to add conditional data to your DataFrame. For example, roulette is a classic casino game that involves a wheel with 38 equal-sized wedges: 18 red wedges, 18 black wedges, and 2 green wedges.

A simulation of your profit playing roulette while betting on red can be done by a conditional that checks if you the result of the game was red:

• If the result was red, you gain $1. (You get your $1 bet back and gain $1 from the casino.)
• If the result was NOT red, you lose $1. (You lose your $1 bet.)

Running this as a simulation:

data = []
for i in range(10000):
  color = random.choice( [
    "red", "red", "red", "red", "red", "red", "red", "red", "red",                    # 9 of 19 outcomes are red
    "black", "black", "black", "black", "black", "black", "black", "black", "black",  # 9 of 19 outcomes are black
    "green",                                                                          # 1 of 19 outcomes are green
  ])

  if color == "red":
    profit = 1
  else:
    profit = -1

  d = { "color": color, "profit": profit }
  data.append(d)
df = pd.DataFrame(data)

df

df["profit"].sum()

-342

Example Walk-Throughs with Worksheets

Video 1: Examples of Conditionals in Python

Practice Questions