datetime.strftime() / datetime.strptime()

from datetime import datetime

# Converts a datetime object to a formatted string.
string = datetime_object.strftime(format_string)

# Creates a datetime object from a formatted string.
dt = datetime.strptime(string, format_string)

datetime_strftime.py

from datetime import datetime

# Display the datetime in various formats.
now = datetime(2025, 4, 15, 9, 30, 0)

# Slash-separated format
print(now.strftime('%Y/%m/%d %H:%M:%S'))
# Output: '2025/04/15 09:30:00'

# ISO 8601 format
print(now.strftime('%Y-%m-%dT%H:%M:%S'))
# Output: '2025-04-15T09:30:00'

# Date only (slash-separated)
print(now.strftime('%Y/%m/%d'))
# Output: '2025/04/15'

# 12-hour format with weekday
print(now.strftime('%Y/%m/%d (%A) %I:%M %p'))
# Output: '2025/04/15 (Tuesday) 09:30 AM'

# Use strptime() to create a datetime object from a string.
date_str = '2025-04-15 09:30:00'
dt = datetime.strptime(date_str, '%Y-%m-%d %H:%M:%S')
print(dt) # Outputs: '2025-04-15 09:30:00'
print(type(dt)) # Outputs: '<class 'datetime.datetime'>'

# Parse a date string in slash-separated format.
date_str2 = '2025/4/15'
dt2 = datetime.strptime(date_str2, '%Y/%m/%d')
print(dt2.year) # Outputs: '2025'
print(dt2.month) # Outputs: '4'

# Convert a date received from a web form.
form_input = '15/04/2025'
dt3 = datetime.strptime(form_input, '%d/%m/%Y')
formatted = dt3.strftime('%Y-%m-%d')
print(formatted) # Outputs: '2025-04-15'

Running the code produces the following output:

python3 datetime_strftime.py
2025/04/15 09:30:00
2025-04-15T09:30:00
2025/04/15
2025/04/15 (Tuesday) 09:30 AM
2025-04-15 09:30:00
<class 'datetime.datetime'>
2025
4
2025-04-15

Common Mistake 1: Confusing strftime and strptime

strftime() converts a datetime object to a string. strptime() creates a datetime object from a string. The names are similar and easy to mix up.

from datetime import datetime

dt = datetime(2025, 4, 15, 9, 30, 0)

# strftime: datetime → string (format time)
date_str = dt.strftime('%Y/%m/%d')
print(date_str) # '2025/04/15'
print(type(date_str)) # <class 'str'>

# strptime: string → datetime (parse time)
dt2 = datetime.strptime('2025/04/15', '%Y/%m/%d')
print(dt2) # 2025-04-15 00:00:00
print(type(dt2)) # <class 'datetime.datetime'>

Common Mistake 2: Confusing uppercase and lowercase format codes

Format codes are case-sensitive and mean different things depending on the case. A particularly common error is mixing up %m (month) and %M (minute).

%m is month (04), %M is minute (30).

from datetime import datetime

dt = datetime(2025, 4, 15, 9, 30, 0)

# using %M (minute) where %m (month) was intended
wrong = dt.strftime('%Y/%M/%d') # accidentally used %M for the month
print(wrong) # '2025/30/15' (wrong value)

The same logic can also be written as:

from datetime import datetime

dt = datetime(2025, 4, 15, 9, 30, 0)

correct = dt.strftime('%Y/%m/%d %H:%M')
print(correct) # '2025/04/15 09:30'

'strftime()' stands for "string format time" and converts a datetime object to a string in any format you specify. 'strptime()' stands for "string parse time" and creates a datetime object from a formatted string. Both functions use the same format codes, so learning them once lets you use both.

The behavior of some format codes may vary slightly by operating system. For example, the code for removing leading zeros from month or day values ('%-m' on Linux) does not work on Windows. If you need to strip leading zeros, it is more portable to convert the string first and then remove them with 'lstrip("0")'.

For creating datetime objects, see 'datetime.datetime() / datetime.date() / datetime.time()'.