How to convert date to datetime in Python?

To convert a date object to a datetime object in Python, you can use the datetime.combine() method or construct a datetime object directly. Below is a detailed explanation with examples.

1. Using datetime.combine()

The datetime.combine() method merges a date object and a time object into a datetime object. If no time is specified, it defaults to midnight (00:00:00).

Example 1: Convert a date to datetime with default time (midnight)

from datetime import date, datetime, time

# Create a date object
today_date = date.today()

# Combine with default time (00:00:00)
today_datetime = datetime.combine(today_date, time())
print(today_datetime)  # Output: 2023-09-21 00:00:00 (depends on today's date)

Example 2: Convert a date to datetime with a custom time

from datetime import date, datetime, time

# Create a date object
custom_date = date(2023, 12, 25)

# Create a custom time (e.g., 14:30:45)
custom_time = time(14, 30, 45)

# Combine into a datetime
custom_datetime = datetime.combine(custom_date, custom_time)
print(custom_datetime)  # Output: 2023-12-25 14:30:45

2. Using the datetime Constructor

You can directly create a datetime object by extracting the year, month, and day from a date object. This also defaults to midnight.

Example 3: Construct datetime from date attributes

from datetime import date, datetime

# Create a date object
my_date = date(2023, 7, 4)

# Convert to datetime using the constructor
my_datetime = datetime(my_date.year, my_date.month, my_date.day)
print(my_datetime)  # Output: 2023-07-04 00:00:00

3. Parsing a Date String to datetime

If you have a date string (e.g., "2023-10-05"), parse it directly into a datetime object using datetime.strptime().

Example 4: Convert a date string to datetime

from datetime import datetime

date_str = "2023-10-05"

# Parse directly into a datetime object
datetime_obj = datetime.strptime(date_str, "%Y-%m-%d")
print(datetime_obj)  # Output: 2023-10-05 00:00:00

Key Notes:

• date vs. datetime:
• A date object holds year, month, and day.
• A datetime object holds year, month, day, hour, minute, second, and microsecond.
• Time Zone Awareness: The examples above create naive datetime objects (no timezone). For timezone-aware conversions, use libraries like pytz or Python 3.9+’s zoneinfo.

Summary of Methods

Method	Use Case
datetime.combine(date, time)	Best for combining a date with a custom time.
datetime(year, month, day)	Simple conversion with default midnight time.
datetime.strptime()	Directly parse a date string to datetime.

By using these methods, you can seamlessly convert between date and datetime objects in Python.