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How to Format Numbers with Thousands Separators and Currency in Python

Presenting numbers clearly, especially large ones, often involves using thousands separators (like commas or spaces) and formatting them as currency.

This guide explores various methods in Python to format numbers with thousands separators and as currency, using f-strings, str.format(), and the locale module.

Formatting Numbers with Thousands Separators​

f-strings provide the most concise and readable way to add a comma as a thousands separator:

my_int = 489985123
result = f'{my_int:,}'
print(result)  # Output: 489,985,123
  • The comma (,) after the colon (:) in the f-string format specifier tells Python to use a comma as the thousands separator.

Using str.format()​

The str.format() method offers an alternative:

my_int = 489985123
result = '{:,}'.format(my_int)
print(result)  # Output: 489,985,123

Using the locale Module (Locale-Aware)​

For formatting based on the user's system locale (which might use different separators like periods), use the locale module and the :n format specifier:

import locale

# Set locale to the user's default setting (can vary)
try:
    # Attempt to set a common locale like en_US.UTF-8 first
    locale.setlocale(locale.LC_ALL, 'en_US.UTF-8')
except locale.Error:
    try:
        # Fallback to the system's default locale
        locale.setlocale(locale.LC_ALL, '')
    except locale.Error:
        print("Warning: Could not set a suitable locale. Using default C locale.")
        locale.setlocale(locale.LC_ALL, 'C') # Fallback to basic C locale

my_int = 489985123
result = f'{my_int:n}'

# Output depends on locale, e.g., '489,985,123' in US, potentially '489.985.123' in others
print(result)
  • locale.setlocale(locale.LC_ALL, '') sets the locale based on the system's environment variables.
  • The :n format specifier tells Python to use the locale-specific thousands separator.

Using Spaces as Separators​

To use spaces instead of commas, replace the comma after formatting:

my_int = 489985123
result_fstring = f'{my_int:,}'.replace(',', ' ')
print(result_fstring) # Output: 489 985 123

# Using locale (result depends on the actual separator used by locale)
import locale
locale.setlocale(locale.LC_ALL, '') # Set locale first
result_locale = f'{my_int:n}'
separator = locale.localeconv().get('thousands_sep', ',') # Get locale separator
result_locale_space = result_locale.replace(separator, ' ')
print(result_locale_space) # Output might be: 489 985 123

Formatting Floats with Thousands Separators and Decimals​

Combine the comma separator with precision formatting for floats:

my_float = 489985.456789

# Comma separator, rounded to 2 decimal places
result_2dp = f'{my_float:,.2f}'
print(result_2dp)  # Output: 489,985.46

# Comma separator, rounded to 3 decimal places
result_3dp = f'{my_float:,.3f}'
print(result_3dp)  # Output: 489,985.457
  • The , enables the thousands separator.
  • .Nf rounds the float to N decimal places.

Formatting Lists of Numbers with Thousands Separators​

Use list comprehensions to format all numbers in a list.

Formatting Lists of Integers​

my_list = [489985123, 123456789, 23456789, 45678901]
formatted_list = [f'{x:,}' for x in my_list]
print(formatted_list)
# Output: ['489,985,123', '123,456,789', '23,456,789', '45,678,901']

Formatting Lists of Floats​

list_of_floats = [489985.456789, 123456.678123, 234567.12345]
formatted_list = [f'{item:,.2f}' for item in list_of_floats]
print(formatted_list)
# Output: ['489,985.46', '123,456.68', '234,567.12']

Formatting Numbers as Currency​

Using f-strings​

Prepend the currency symbol and use standard number formatting:

my_float = 15467.3
result = f'${my_float:,.2f}'    # Add $ sign, comma separator, 2 decimal places
print(result)                   # Output: $15,467.30

# Without thousands separator
result_no_comma = f'${my_float:.2f}'
print(result_no_comma)          # Output: $15467.30

Using locale.currency() (Locale-Aware)​

The locale.currency() function provides locale-aware currency formatting:

import locale

# Set locale - IMPORTANT: Ensure the locale is available on your system
try:
    # Try a common US locale
    locale.setlocale(locale.LC_ALL, 'en_US.UTF-8')
except locale.Error:
    try:
        # Fallback to system default
        locale.setlocale(locale.LC_ALL, '')
    except locale.Error:
        print("Warning: Could not set locale. Currency formatting might be basic.")
        locale.setlocale(locale.LC_ALL, 'C')

my_float = 15467.3
result_grouped = locale.currency(my_float, grouping=True) # With grouping (e.g., commas)
print(result_grouped)   # Output (depends on locale): $15,467.30

result_nogroup = locale.currency(my_float, grouping=False) # Without grouping
print(result_nogroup)   # Output (depends on locale): $15467.30

result_nosymbol = locale.currency(my_float, grouping=True, symbol=False) # Without currency symbol
print(result_nosymbol)  # Output (depends on locale): 15,467.30
  • locale.currency() uses the current locale settings to format the number, including the correct currency symbol and separators.
  • The grouping=True argument enables the thousands separator according to the locale.
  • The symbol=True (default) includes the locale's currency symbol.

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