Plotting with numpy and pylab with date strings as x-labels

You can pass any list of strings or numbers as the x axis argument to the plot call and it will try to use them for x axis labels. Here is a basic working example showing how to generate a range of dates and use them in the graph. Because two different date formats are used in the question, DD/MM/YYYY and M/D/YYYY, I provided an example of each.

Here is the code:

import matplotlib.pylab as plt
import datetime

# Define some sample data
my_data = [x ** 3 / 100 - 2 * x ** 2 / 10 + x / 2 + 4 for x in range(20)]
# The first date in the data
start_date = datetime.datetime(1999, 1, 1)
# Generate a new date for each subsequent datapoint
dates = [start_date + datetime.timedelta(x) for x in range(len(my_data))]

# Generate the graphs for the two representations described in the questions
for name, x_labels in [
    ('As written', [f'{date.day:02}/{date.month:02}/{date.year:04}' for date in dates]),
    ('As the example', [f'{date.month}/{date.day}/{date.year}' for date in dates]),
]:
    plt.title(name)
    # matplotlib will automatically use the text has the x-axis labels
    plt.plot(x_labels, my_data)
    # Rotate the labels so they are legible without overlapping
    plt.xticks(rotation=60)
    # Re-scale the window so that everything fits
    plt.tight_layout()
    plt.show()

And here are the graphs it generated: