Plotting with Dates

Matplotlib is a Python library for creating charts and visualizations — and it understands real calendar dates, so a list of datetime objects becomes a properly spaced, neatly labelled time axis.

Learn Plotting with Dates in our free Matplotlib course — a beginner-friendly interactive lesson with worked examples, a practice exercise and a quick…

Part of the free Matplotlib course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

In this lesson you'll build date objects, plot them on the x-axis, format the tick labels with matplotlib.dates, and fix overlapping labels with autofmt_xdate().

Build your dates with Python's datetime module, then pass that list as the x values. Matplotlib recognizes the date objects and lays them out on a proper time axis automatically.

What you'll see: a line rising from January to April, with the four dates correctly spaced along the bottom. Matplotlib spaces them by actual time, not just by position in the list.

To control how the dates are written, import matplotlib.dates as mdates and attach a DateFormatter to the x-axis. The format string uses the same codes as Python's strftime — for example '%b %Y' renders "Jan 2024".

What you'll see: the same trend line, but now the x-axis ticks read "Jan 2024", "Feb 2024", and so on instead of raw numbers — clear, human-readable month labels.

When you have many dates, the labels collide and become unreadable. One call — fig.autofmt_xdate() — rotates and right-aligns the date labels so they fit neatly along the axis.

What you'll see: a full-year curve with all twelve month labels tilted at an angle along the bottom, neatly right-aligned so none of them overlap — even though there are many of them.

Replace each ___ to plot dates and format them as "Jan 2025".

You passed date strings , not date objects. Build them with date(2024, 1, 1) from the datetime module.

Call fig.autofmt_xdate() to rotate them, or use a coarser DateFormatter.

Plot seven daily temperatures, label the axis as "Jun 10" style days, and rotate them.

Lesson 14 complete — you can plot time itself!

You built date objects, plotted them on a time axis, formatted the ticks with DateFormatter, and tamed crowded labels with autofmt_xdate().

🚀 Up next: Twin Axes & Secondary Y — show two different scales on one chart.

Practice quiz

Can Matplotlib plot Python date objects directly on the x-axis?

  • Yes — it recognizes them and spaces them by time
  • No, you must convert to strings
  • Only with pandas
  • Only integers work

Answer: Yes — it recognizes them and spaces them by time. Pass a list of date/datetime objects and Matplotlib lays them out on a time axis.

What is the standard import alias for the date-tools module?

  • import matplotlib.dates as dt
  • import matplotlib.dates as mdates
  • import mdates
  • from matplotlib import dates as d

Answer: import matplotlib.dates as mdates. The conventional alias is mdates: import matplotlib.dates as mdates.

Which class formats date tick labels?

  • mdates.DateLocator
  • mdates.AutoDate
  • mdates.DateFormatter
  • mdates.TimeAxis

Answer: mdates.DateFormatter. mdates.DateFormatter('%b %Y') controls how dates are written.

Which call attaches a formatter to the x-axis?

  • ax.format_xaxis()
  • ax.set_format()
  • plt.dateformat()
  • ax.xaxis.set_major_formatter(...)

Answer: ax.xaxis.set_major_formatter(...). ax.xaxis.set_major_formatter(mdates.DateFormatter(...)) applies the format.

What does the format code %b produce?

  • The short month name (e.g. Jan)
  • The full year
  • The day number
  • The weekday

Answer: The short month name (e.g. Jan). %b is the abbreviated month name, the same strftime code Python uses.

What does %Y produce in a DateFormatter string?

  • The two-digit year
  • The four-digit year
  • The month
  • The hour

Answer: The four-digit year. %Y is the four-digit year, e.g. 2024.

Which call rotates crowded date labels so they don't overlap?

  • ax.rotate()
  • plt.tilt()
  • fig.autofmt_xdate()
  • ax.spread_labels()

Answer: fig.autofmt_xdate(). fig.autofmt_xdate() rotates and right-aligns the date labels.

Why might dates show as plain numbers instead of dates?

  • The figure is too small
  • autofmt was called
  • viridis was used
  • You passed date strings instead of date objects

Answer: You passed date strings instead of date objects. Build real date objects with date(2024, 1, 1), not strings.

Which import gives you the date type?

  • from datetime import date
  • import dates
  • from time import date
  • import calendar

Answer: from datetime import date. from datetime import date provides the date class.

What does the format string '%b %Y' render for January 2024?

  • 2024-01
  • Jan 2024
  • 01/2024
  • January

Answer: Jan 2024. %b %Y produces the short month and four-digit year, e.g. 'Jan 2024'.