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Finding the Weekday of a Date in Python – Complete Guide for Data Science 2026

Determining the weekday (Monday, Tuesday, etc.) of a date is one of the most common operations in data science. It is used for creating day-of-week features, analyzing weekly seasonality, building business calendars, and generating insightful reports. In 2026, Python offers several clean and efficient ways to get the weekday of any date.

TL;DR — Recommended Methods

date.weekday() → 0 = Monday, 6 = Sunday
date.isoweekday() → 1 = Monday, 7 = Sunday
date.strftime("%A") → Full day name ("Monday")
pandas .dt.day_name() and .dt.weekday → vectorized for DataFrames

1. Pure Python – datetime.date

from datetime import date

d = date(2026, 3, 19)

print(d.weekday())          # 3 → Thursday (0=Monday)
print(d.isoweekday())       # 4 → Thursday (1=Monday)
print(d.strftime("%A"))     # "Thursday"
print(d.strftime("%a"))     # "Thu"

2. pandas – Vectorized Weekday Extraction

import pandas as pd

df = pd.read_csv("sales_data.csv", parse_dates=["order_date"])

# Add weekday features
df["weekday_number"] = df["order_date"].dt.weekday          # 0 = Monday
df["day_name"] = df["order_date"].dt.day_name()             # "Thursday"
df["day_name_short"] = df["order_date"].dt.day_name(locale="en_US.utf8").str[:3]
df["is_weekend"] = df["order_date"].dt.weekday.isin([5, 6])

print(df[["order_date", "day_name", "is_weekend"]].head())

3. Real-World Data Science Examples

# Example 1: Weekly seasonality analysis
weekly_sales = df.groupby(df["order_date"].dt.day_name())["amount"].mean()

# Example 2: Business-day vs weekend filtering
business_days = df[~df["order_date"].dt.weekday.isin([5, 6])]
weekend_sales = df[df["order_date"].dt.weekday.isin([5, 6])]

4. Best Practices in 2026

Use pandas .dt.day_name() and .dt.weekday for large DataFrames
Prefer .weekday() (0=Monday) for most calculations
Use strftime("%A") only when you need the full name as a string
Always work with timezone-aware datetimes before extracting weekday
Create is_weekend feature early in your pipeline

Conclusion

Finding the weekday of a date is simple yet extremely valuable in data science. In 2026, combine Python’s date.weekday() / strftime() with pandas’ vectorized .dt accessor to create powerful day-of-week features, analyze weekly patterns, and build smarter time-based models.

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