time-formatting.md

Python by Example: Time Formatting

You often need to display dates as strings or parse strings into dates. Use strftime to format a datetime as a string and strptime to parse a string into a datetime. Format codes like %Y (year), %m (month), %d (day) are standard. The same codes work for both formatting and parsing.

What you'll learn:

• strftime — datetime to string
• strptime — string to datetime
• Common format codes

from datetime import datetime

now = datetime.now()

# Format: datetime -> string
formatted = now.strftime("%Y-%m-%d %H:%M:%S")
print(formatted)

# Custom format
print(now.strftime("%A, %B %d, %Y"))

# Parse: string -> datetime
s = "2025-02-10 14:30:00"
parsed = datetime.strptime(s, "%Y-%m-%d %H:%M:%S")
print(parsed)

%Y is 4-digit year; %m is month; %d is day; %H, %M, %S are hour, minute, second. %A is full weekday name; %B is full month name.

To run this program:

$ python source/time-formatting.py
2025-02-10 14:30:00          # varies by execution time
Monday, February 10, 2025    # varies by locale
2025-02-10 14:30:00          # parsed—always the same

The first two lines depend on when and where you run the script; the third is deterministic.

Tip: Use ISO format %Y-%m-%d for filenames and APIs—it sorts correctly.

Try it: Parse a date string and format it in a different style.

Source: time-formatting.py

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