Converting Date Strings to Timestamps in Python

Often, you’ll encounter date information stored as strings. To perform calculations or comparisons with dates, it’s often necessary to convert these strings into numerical timestamps, representing the number of seconds since the Unix epoch (January 1, 1970, 00:00:00 UTC). This tutorial will guide you through the process of converting date strings to timestamps in Python.

Understanding the Core Concepts

A timestamp is a numerical representation of a point in time. In Python, it’s commonly represented as a floating-point number indicating seconds since the epoch. The datetime module is the primary tool for working with dates and times. The key is to parse the date string into a datetime object and then convert that object into a timestamp.

Parsing Date Strings with `strptime()`

The strptime() method (string parse time) is fundamental to this process. It takes two arguments:

The date string you want to convert.
A format string that specifies how the date is represented in the string.

Here’s a breakdown of common format codes:

%d: Day of the month (01-31)
%m: Month as a number (01-12)
%Y: Year with century (e.g., 2023)
%H: Hour (00-23)
%M: Minute (00-59)
%S: Second (00-59)

For example, if your date string is in the format "01/12/2011", the format string would be "%d/%m/%Y".

from datetime import datetime

date_string = "01/12/2011"
format_string = "%d/%m/%Y"

datetime_object = datetime.strptime(date_string, format_string)

print(datetime_object)

This code will output a datetime object representing December 1st, 2011.

Converting to a Timestamp

Once you have the datetime object, you can convert it to a timestamp using the .timestamp() method. This method returns a floating-point number representing the timestamp.

from datetime import datetime

date_string = "01/12/2011"
format_string = "%d/%m/%Y"

datetime_object = datetime.strptime(date_string, format_string)
timestamp = datetime_object.timestamp()

print(timestamp) # Output: 1322697600.0

Handling Timezones

By default, datetime.timestamp() uses the local timezone. If you need the timestamp in UTC, you can explicitly set the timezone information before converting. Here’s how:

from datetime import datetime, timezone

date_string = "01/12/2011"
format_string = "%d/%m/%Y"

datetime_object = datetime.strptime(date_string, format_string)
utc_datetime = datetime_object.replace(tzinfo=timezone.utc)
utc_timestamp = utc_datetime.timestamp()

print(utc_timestamp)

The .replace(tzinfo=timezone.utc) method adds UTC timezone information to the datetime object.

Alternative Approach: Using `time.mktime()`

While .timestamp() is generally preferred, you can also use the time.mktime() function from the time module. However, time.mktime() expects a time tuple, so you need to convert the datetime object to a tuple first using .timetuple().

import time
from datetime import datetime

date_string = "01/12/2011"
format_string = "%d/%m/%Y"

datetime_object = datetime.strptime(date_string, format_string)
timestamp = time.mktime(datetime_object.timetuple())

print(timestamp)

Important Considerations

Format String Accuracy: The format string must accurately match the format of the input date string. If there’s a mismatch, strptime() will raise a ValueError.
Timezone Awareness: Be mindful of timezones. If your application requires consistent timestamps, always work in UTC.
Error Handling: Consider adding error handling (e.g., try...except) to handle potential ValueError exceptions that may occur if the input date string is invalid.