x-axis labels with Matplotlib

[Mark17]

Hopefully this isn't too hard to follow.

Fri_2017 is a list of the first 20 Fridays in 2017 as type datetime.datetime .

I also have this:

for i in range(20):
    random_pnl_list.append(random.randint(-1000,1000))
cumul_pnl_from_random = list(np.cumsum(random_pnl_list))

Now... when I do this in matplotlib:

plt.plot(Fri_2017,cumul_pnl_from_random)

I get x-axis labels at the first and 22nd of the first five months (e.g. 2017-01-01, 2017-01-22, 2017-02-01... 2017-05-01, 2017-05-22). How is this determined--both format and those two particular dates of every month?

I also have this line:

converted_Fri_2017 = [d.strftime('%Y-%m-%d') for d in Fri_2017]

When I do:

plt.plot(converted_Fri_2017,cumul_pnl_from_random)

I get x-axis labels of same format as above (yyyy-mm-dd) but every Friday from 1/6/17 through 5/19/17 (20 total labels). Why the difference?