Format Dates and Times in Python

When you work with dates and times in Python, you often need to display them to users or read date strings from files and APIs. The datetime module covers both directions: strftime formats a date as a string, and strptime parses a string into a datetime object.

python

from datetime import datetime
 
now = datetime.now()
print(now.strftime("%B %d, %Y"))  # July 12, 2026

strftime stands for "string from time". You pass a format string full of percent codes, and Python replaces each code with the matching part of the date. Here %B becomes the full month name, %d the zero-padded day, and %Y the four-digit year.

strftime: format a date as a string

The strftime method works on the date, datetime, and time objects you create when you work with dates and times in Python. You build a format string by mixing literal characters with format codes that start with a percent sign.

python

from datetime import datetime
 
event = datetime(2026, 12, 25, 18, 30)
 
print(event.strftime("%Y-%m-%d"))   # 2026-12-25
print(event.strftime("%A, %B %d"))  # Friday, December 25
print(event.strftime("%I:%M %p"))   # 06:30 PM

Each format code pulls one piece of information out of the datetime. Literal characters such as dashes, commas, colons, and spaces pass through to the output unchanged.

Common strftime format codes

This table covers the codes you will use most often in real programs, with the value each one produces for Sunday, July 12, 2026 at 14:30:05.

You can combine the codes in any order to build the exact output you need. A few patterns show up constantly in real code:

python

from datetime import datetime
 
dt = datetime(2026, 7, 12, 14, 30, 5)
 
print(dt.strftime("%m/%d/%Y"))  # 07/12/2026
print(dt.strftime("%d-%b-%Y"))  # 12-Jul-2026
print(dt.strftime("%A, %B %d, %Y at %I:%M %p"))  # Sunday, July 12, 2026 at 02:30 PM

The first two are compact numeric styles, and the third is a full human-readable sentence built from the same building blocks.

strptime: parse a string into a datetime

strptime, short for "string parse time", does the reverse. It reads a date string plus a format that describes the string's structure, and returns a datetime object.

python

from datetime import datetime
 
parsed = datetime.strptime("2026-07-12", "%Y-%m-%d")
print(parsed)        # 2026-07-12 00:00:00
print(type(parsed))  # <class 'datetime.datetime'>

The format "%Y-%m-%d" tells Python to expect a four-digit year, a dash, a two-digit month, another dash, and a two-digit day. Any time component you do not supply defaults to zero, which is why the result lands at midnight.

Parsing different date formats

The format string must match the input exactly, because spaces, punctuation, and code order all matter.

python

from datetime import datetime
 
print(datetime.strptime("12/07/2026", "%d/%m/%Y"))      # 2026-07-12 00:00:00
print(datetime.strptime("July 12, 2026", "%B %d, %Y"))  # 2026-07-12 00:00:00
print(datetime.strptime("12-Jul-2026 14:30", "%d-%b-%Y %H:%M"))  # 2026-07-12 14:30:00

Each call produces the same date, July 12, 2026, but reads a different input style. The third call also captures the time because its format includes the hour and minute codes.

A mismatch between the string and the format is a hard error rather than a wrong guess. When they do not line up, strptime raises a ValueError:

python

from datetime import datetime
 
datetime.strptime("2026-07-12", "%d/%m/%Y")
# ValueError: time data '2026-07-12' does not match format '%d/%m/%Y'

The input uses dashes but the format expects slashes, so parsing fails immediately. Failing loudly is useful here, because a silent wrong guess would corrupt your data.

ISO 8601 format

The ISO 8601 standard, YYYY-MM-DD for dates and YYYY-MM-DDTHH:MM:SS for datetimes, is the most common machine-readable date format. The Python standard library supports it directly, with no format codes needed.

python

from datetime import date, datetime
 
print(date.today().isoformat())          # 2026-07-12
print(date.fromisoformat("2026-12-25"))  # 2026-12-25
print(datetime.fromisoformat("2026-07-12T14:30:00"))  # 2026-07-12 14:30:00

isoformat produces the standard string and fromisoformat parses it back. Use this pair when saving dates to JSON, writing to a database, or exchanging data between systems, because the format is unambiguous and widely supported.

Practical example: parsing a user-supplied date

A common real-world task is accepting a date string that may arrive in one of several styles. Trying a list of formats in order handles that cleanly.

python

from datetime import datetime
 
def parse_date(date_string):
    formats = ["%Y-%m-%d", "%m/%d/%Y", "%d-%b-%Y"]
    for fmt in formats:
        try:
            return datetime.strptime(date_string, fmt).date()
        except ValueError:
            continue
    raise ValueError(f"Cannot parse date: {date_string}")
 
print(parse_date("07/12/2026"))  # 2026-07-12

The function tries each format until one succeeds, then returns a date object. If nothing matches, it raises its own error, which is the right behavior when the input truly cannot be understood.

Building readable timestamps

Format codes shine when you need timestamps for logs, filenames, or display text.

python

from datetime import datetime
 
now = datetime.now()
 
print(now.strftime("[%Y-%m-%d %H:%M:%S]"))       # [2026-07-12 14:30:05]
print(now.strftime("report_%Y%m%d_%H%M%S.txt"))  # report_20260712_143005.txt
print(now.strftime("%A, %B %d, %Y"))             # Sunday, July 12, 2026

The first line is a typical log prefix and the last is a display style. For filenames, avoid spaces and colons, and prefer compact codes like %Y%m%d so the names sort correctly.

Common mistakes

Four mistakes cause most date formatting bugs in practice.

Swapping %m and %d. The format %m/%d/%Y means month first, in the US style, while %d/%m/%Y means day first, used in most other regions. The wrong order often produces a valid-looking but wrong date, so always confirm which style your input uses.

Using %y instead of %Y. Two-digit years are ambiguous about the century. Prefer %Y unless you are forced to handle two-digit year data.

Forgetting that strptime needs an exact match. A single misplaced space or wrong separator raises a ValueError. When parsing fails, print the input string and the format string side by side to spot the mismatch.

Calling strptime on an instance. strptime is a class method, so write datetime.strptime(text, fmt) rather than calling it on an existing datetime value.