5 Best Ways to Convert an Array of Datetimes into an Array of Strings with UTC Timezone in Python

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💡 Problem Formulation: Python developers often encounter the need to manipulate datetime objects. For instance, when dealing with an array of datetime objects, one might need to convert them into an array of string representations set in UTC timezone. This conversion is necessary for consistent time-related data processing across different time zones. Our input could be an array like [datetime.datetime(2021, 7, 21, 12), datetime.datetime(2021, 7, 22, 12)] and the desired output an array of strings like ["2021-07-21T12:00:00Z", "2021-07-22T12:00:00Z"].

Method 1: Using pytz and strftime()

This method leverages the pytz library to localize datetimes to UTC before converting them to strings. The strftime() function is then used to format the datetime object into a UCT timezone string. The pytz library provides time zone information and allows datetime objects to be converted to a preferred timezone.

Here’s an example:

import datetime
import pytz

datetimes = [datetime.datetime(2021, 7, 21, 12), datetime.datetime(2021, 7, 22, 12)]
utc_strings = [dt.replace(tzinfo=pytz.utc).strftime("%Y-%m-%dT%H:%M:%SZ") for dt in datetimes]

Output:

["2021-07-21T12:00:00Z", "2021-07-22T12:00:00Z"]

In the code snippet, the datetime objects are first associated with UTC timezone using replace(tzinfo=pytz.utc), ensuring the time is set to UTC. The strftime() function then converts each datetime object to a formatted string that includes the UTC indicator ‘Z’ at the end.

Method 2: Using datetime.timezone.utc and strftime()

The datetime.timezone.utc attribute from the standard Python datetime module can be used as a timezone aware UTC object. When combined with strftime() for formatting, it provides a straightforward way to convert datetime objects to UTC strings without the need for an external library like pytz.

Here’s an example:

from datetime import datetime, timezone

datetimes = [datetime(2021, 7, 21, 12), datetime(2021, 7, 22, 12)]
utc_strings = [dt.astimezone(timezone.utc).strftime("%Y-%m-%dT%H:%M:%SZ") for dt in datetimes]

Output:

["2021-07-21T12:00:00Z", "2021-07-22T12:00:00Z"]

Here, astimezone(timezone.utc) is used to convert the naive datetime object to timezone-aware UTC datetime before formatting into a string. This is a pure Python approach without dependencies on external libraries.

Method 3: Using isoformat() and Slicing Off Timezone Info

This method uses the built-in isoformat() method combined with string manipulation. Although isoformat() includes timezone information by default, you can use simple string slicing to add a ‘Z’ character at the end to indicate UTC time.

Here’s an example:

from datetime import datetime, timezone

datetimes = [datetime(2021, 7, 21, 12).replace(tzinfo=timezone.utc), datetime(2021, 7, 22, 12).replace(tzinfo=timezone.utc)]
utc_strings = [dt.isoformat()[:-6] + "Z" for dt in datetimes]

Output:

["2021-07-21T12:00:00Z", "2021-07-22T12:00:00Z"]

The replace(tzinfo=timezone.utc) method is called on each datetime object to make it UTC timezone-aware, and then isoformat() generates a string that is UTC-encoded. String slicing is used to strip off the unwanted microseconds and timezone info, and a ‘Z’ is appended at the end manually.

Method 4: Using pendulum Library

The pendulum library simplifies datetime manipulation and provides easier timezone conversion and formatting. When the pendulum object is converted to a string, it defaults to an ISO 8601 format including UTC time.

Here’s an example:

import pendulum

datetimes = [pendulum.datetime(2021, 7, 21, 12), pendulum.datetime(2021, 7, 22, 12)]
utc_strings = [dt.in_timezone('UTC').to_iso8601_string() for dt in datetimes]

Output:

["2021-07-21T12:00:00+00:00", "2021-07-22T12:00:00+00:00"]

Each datetime object is first converted to a pendulum object, localized to UTC using in_timezone('UTC'), and then converted to a string with to_iso8601_string(). The resultant string includes the +00:00 timezone offset which indicates UTC time.

Bonus One-Liner Method 5: Using List Comprehension with datetime.isoformat()

If you’re looking for a quick one-liner that does not require external libraries, you can use isoformat() in conjunction with list comprehension. The naive datetime object is combined with the ‘Z’ character to signify UTC time.

Here’s an example:

from datetime import datetime

datetimes = [datetime(2021, 7, 21, 12), datetime(2021, 7, 22, 12)]
utc_strings = [dt.isoformat() + "Z" for dt in datetimes]

Output:

["2021-07-21T12:00:00Z", "2021-07-22T12:00:00Z"]

This one-liner takes advantage of the naiveté of the input datetime objects, appending ‘Z’ to the isoformatted string signifies they are meant to represent UTC. However, this method should be used with caution if the original datetimes are not already in UTC.

Summary/Discussion

  • Method 1: Using pytz Library. Strengths: Provides accurate timezone conversions for complex cases. Weaknesses: Requires an external library.
  • Method 2: Using datetime.timezone.utc. Strengths: Built-in Python functionality, no external dependencies. Weaknesses: Slightly less straightforward than isoformat().
  • Method 3: Using isoformat() and Slicing. Strengths: Quick and easy, utilizes built-in methods. Weaknesses: Manual string manipulation may introduce errors if not done correctly.
  • Method 4: Using pendulum Library. Strengths: Simplifies datetime manipulation with intuitive methods. Weaknesses: Requires an external library.
  • Method 5: Bonus One-Liner. Strengths: Simplest and quickest method, no external dependencies. Weaknesses: Assumes naive datetime is in UTC, may not always be appropriate.