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Tutorial Reference

How to Reformat Datetime Strings in Python

Learn how to convert datetime strings between formats in Python using strptime() and strftime() for database operations, API communication, and data integration.

Converting dates between formats is essential for data integration, API communication, and database operations. Whether you're transforming "December 31, 2024" into "2024-12-31" for database storage or converting ISO timestamps into human-friendly displays, Python's datetime module provides reliable tools for parsing and reformatting date strings. This guide walks you through the core techniques and common patterns for datetime string manipulation.

The Parse-Then-Format Pattern

Reformatting dates requires two steps: parsing the original string into a datetime object, then formatting that object into your desired output. The strptime() method handles parsing, while strftime() handles formatting:

from datetime import datetime

original = "31-Dec-2025 23:59:59"

dt = datetime.strptime(original, "%d-%b-%Y %H:%M:%S")

reformatted = dt.strftime("%Y/%m/%d %H:%M")

print(f"Original: {original}")
print(f"Reformatted: {reformatted}")

Output:

Original: 31-Dec-2025 23:59:59
Reformatted: 2025/12/31 23:59

Essential Format Codes

Understanding format codes is crucial for accurate parsing and formatting:

Code Meaning Example
%Y 4-digit year 2024
%y 2-digit year 24
%m Month (zero-padded) 05
%B Full month name December
%b Abbreviated month Dec
%d Day of month 31
%H Hour (24-hour) 23
%I Hour (12-hour) 11
%M Minute 59
%S Second 45
%p AM/PM PM

Common Format Conversions

from datetime import datetime

dt = datetime.strptime("2025-12-31 14:30:00", "%Y-%m-%d %H:%M:%S")

print(dt.strftime("%d/%m/%Y"))           # 31/12/2025
print(dt.strftime("%B %d, %Y"))          # December 31, 2025
print(dt.strftime("%Y%m%d"))             # 20251231
print(dt.strftime("%I:%M %p"))           # 02:30 PM
print(dt.strftime("%A, %B %d"))          # Wednesday, December 31
print(dt.strftime("%Y-%m-%dT%H:%M:%SZ")) # 2025-12-31T14:30:00Z

Handling Multiple Input Formats

When processing data from various sources, you may encounter different date formats:

from datetime import datetime

def parse_flexible_date(date_string):
    """Try multiple formats to parse a date string."""
    formats = [
        "%Y-%m-%d",
        "%d/%m/%Y",
        "%m/%d/%Y",
        "%B %d, %Y",
        "%d-%b-%Y",
        "%Y%m%d"
    ]
    
    for fmt in formats:
        try:
            return datetime.strptime(date_string, fmt)
        except ValueError:
            continue
    
    raise ValueError(f"Unable to parse date: {date_string}")


dates = ["2025-12-31", "31/12/2025", "December 31, 2025"]

for date_str in dates:
    dt = parse_flexible_date(date_str)
    print(f"{date_str} → {dt.strftime('%Y-%m-%d')}")

Output:

2025-12-31 → 2025-12-31
31/12/2025 → 2025-12-31
December 31, 2025 → 2025-12-31

Batch Processing with Pandas

For large datasets, Pandas offers optimized datetime handling:

import pandas as pd

data = {
    "event": ["Launch", "Update", "Release"],
    "date": ["2024-01-15", "2024-06-30", "2024-12-31"]
}

df = pd.DataFrame(data)

df["date"] = pd.to_datetime(df["date"])

df["formatted"] = df["date"].dt.strftime("%B %d, %Y")

print(df)

Reusable Reformatting Function

from datetime import datetime

def reformat_date(date_string, input_format, output_format):
    """
    Convert a date string from one format to another.
    
    Args:
        date_string: The original date string
        input_format: Format of the input string
        output_format: Desired output format
    
    Returns:
        Reformatted date string
    """
    dt = datetime.strptime(date_string, input_format)
    return dt.strftime(output_format)


print(reformat_date("31-12-2025", "%d-%m-%Y", "%Y/%m/%d"))

print(reformat_date("Dec 31, 2025", "%b %d, %Y", "%Y-%m-%d"))

Working with Timezones

For timezone-aware datetime handling:

from datetime import datetime
from zoneinfo import ZoneInfo  # Python 3.9+

dt = datetime.strptime("2025-12-31 14:30:00", "%Y-%m-%d %H:%M:%S")
dt_utc = dt.replace(tzinfo=ZoneInfo("UTC"))

dt_eastern = dt_utc.astimezone(ZoneInfo("America/New_York"))

print(f"UTC: {dt_utc.strftime('%Y-%m-%d %H:%M %Z')}")
print(f"Eastern: {dt_eastern.strftime('%Y-%m-%d %H:%M %Z')}")

Output:

UTC: 2025-12-31 14:30 UTC
Eastern: 2025-12-31 09:30 EST

By mastering the parse-and-format pattern, you can reliably convert datetime strings between any formats required by your databases, APIs, or user interfaces.

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