Python Ternary Operator (Conditional Expression): How to Write if-else in One Line

In programming, we frequently encounter situations where we want to change the value assigned to a variable based on a specific condition. Usually, we use if and else statements, but Python provides a syntax to write this concisely in a single line. While this is often called the “ternary operator” in other languages, Python’s official documentation refers to it as a “conditional expression.”

This article explains how to write conditional expressions and how to distinguish their use from standard if statements.

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Basic Syntax of the Ternary Operator (Conditional Expression)

Python’s conditional expression follows a word order that reads naturally like an English sentence.

Syntax:

value_if_true if condition else value_if_false

If the condition is True, the value on the left is evaluated (adopted). If False, the value on the right (after else) is evaluated.

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Specific Usage Examples

As an example, let’s create a program that determines shipping fees based on a user’s membership rank.

1. Writing with Standard if-else

First, let’s look at the traditional way of writing this.

member_rank = "Gold"
shipping_fee = 0

# If rank is Gold, shipping is free (0), otherwise 500
if member_rank == "Gold":
    shipping_fee = 0
else:
    shipping_fee = 500

print(f"Shipping Fee: {shipping_fee} yen")

This logic is correct, but it takes 4 lines of code just for a simple value assignment.

2. Writing with the Ternary Operator

Now, let’s rewrite the same logic using a conditional expression.

member_rank = "Gold"

# Writing if-else in one line
shipping_fee = 0 if member_rank == "Gold" else 500

print(f"Shipping Fee: {shipping_fee} yen")

Output:

Shipping Fee: 0 yen

It became very simple. The logic “The shipping fee is 0 if the rank is Gold, else it is 500″ is expressed in a single line.

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Another Example: Even or Odd Check

Here is an example of switching strings based on a calculation result.

number = 15

# If the remainder of division by 2 is 0, it is "Even", otherwise "Odd"
result_type = "Even" if number % 2 == 0 else "Odd"

print(f"{number} is {result_type}")

Output:

15 is Odd

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Note: Readability

While ternary operators are helpful for shortening code, overusing them can actually hurt readability. Specifically, putting a conditional expression inside another one (nesting) is not recommended.

# Not Recommended: Nested ternary operators (Very hard to read)
score = 75
grade = "A" if score >= 90 else "B" if score >= 70 else "C"

For complex branching like this, it is kinder to the reader to use the standard if ... elif ... else syntax.

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Summary

• In Python, you can use the value1 if condition else value2 syntax to assign values based on conditions in one line.
• This is called a “conditional expression” or “ternary operator.”
• Use it to simplify code for simple conditional assignments.
• For complex branching, stick to standard if statements to maintain readability.