Using f-string for conditional formatting in Python

# Using f-string for conditional formatting in Python

Use a ternary operator to use f-strings for conditional formatting.

The ternary operator will return the value to the left if the condition is met, otherwise, the value to the right is returned.

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my_str = 'bobbyhadz.com'

# ✅ f-string formatting with a condition

result = f'Result: {my_str.upper() if len(my_str) > 1 else my_str.capitalize()}'
print(result)  # 👉️ Result: BOBBYHADZ.COM

The example uses the ternary operator to check for conditions in f-strings.

Formatted string literals (f-strings) let us include expressions inside of a string by prefixing the string with f.

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my_str = 'is subscribed:'
my_bool = True

result = f'{my_str} {my_bool}'
print(result)  # 👉️ is subscribed: True

Make sure to wrap expressions in curly braces - {expression}.

The ternary operator is very similar to an inline if/else statement.

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my_str = 'hello'


result = f'Result: {my_str.upper() if len(my_str) > 1 else my_str.capitalize()}'
print(result)  # 👉️ Result: HELLO

The example checks if the length of the string is greater than 1 and if it is, the ternary operator calls the upper() method on the string and returns the result.

If the condition is not met, the else statement runs.

Here is a very simple example of using the ternary operator to check for a condition.

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my_bool = True


result = 'hello' if my_bool else 'bye'
print(result)  # 👉️ 'hello'

If the condition is met, the value to the left is returned, otherwise the value to the right is returned.

# Using the format-specific mini-language conditionally in an f-string

If you need to use the format-specific mini-language in an f-string, you have to use two sets of curly braces.

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my_num = 4.56789
result = f'The number is: {my_num:{".2f" if my_num > 1 else ""}}'

print(result)  # 👉️ The number is: 4.57

Here is what the f-string would look like without a condition.

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my_float = 4.56789

my_str_1 = f'{my_float:.2f}'
print(my_str_1)  # 👉️ 4.57

The first set of curly braces is used to evaluate the variable.

# Alternate between single and double quotes

A very important thing to note is that we are using single quotes to wrap the f-string and double quotes to wrap the strings within.

If you use nested quotes of the same type, you will get an error due to terminating the f-string string prematurely.

The following example checks if the my_bool variable stores a truthy value in the f-string.

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my_num = 4.56789

my_bool = True

result = f'{my_num:{".2f" if my_bool else ""}}'
print(result)  # 👉️ 4.57

If the my_bool variable stores a truthy value, the number gets formatted to 2 decimal places, otherwise an empty string is returned.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

• Check if a String contains a Number in Python
• Check if a string contains any Uppercase letters in Python
• How to Check if a String contains Vowels in Python
• Check if a string does NOT contain substring in Python
• Check if String ends with a Substring using Regex in Python
• Check if List contains a String case-insensitive in Python
• Check if String starts with any Element from List in Python
• Check if a String starts with a Number or Letter in Python