Today I learned how to set different thousands separators using string formatting.

Thousands separators

When doing string formatting with big integers, you may want to include thousands separators to make numbers easier to read. You can add commas, underscores, or a locale-appropriate separator, using the specifiers ,, _, or n, respectively:

bignum = 123541241234

print(f"Big money ${bignum:,}")
# Big money $123,541,241,234

print(f"Big money ${bignum:_}")
# Big money $123_541_241_234

print(f"Big money ${bignum:n}")
# Big money $123541241234

When you specify that you are printing binary (b), octal (o), or hexadecimal digits (x/X), _ can be used to insert underscores every four digits:

bits = 0b10_0000_1111_0110

print(f"{bits:b}")   # 10000011110110
print(f"{bits:_b}")  # 10_0000_1111_0110

hex_value = 0xfa35_de98

print(f"{hex_value:x}")   # fa35de98
print(f"{hex_value:_x}")  # fa35_de98

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References

• Python 3.13 Documentation, Format Specification Mini-Language https://docs.python.org/3/library/string.html#formatspec [last accessed 26-05-2025];