import numpy.random as npr
import numpy as np
import matplotlib.pyplot as plt
import datetime
import matplotlib.dates as mdates


observations=30
mean_days=365
intervals=npr.exponential(mean_days, observations)

dates=[datetime.date(2020, 1, 1)]
for i in intervals:
    dates.append(dates[-1]+datetime.timedelta(days=i))
    
levels = np.tile([-5, 5, -3, 3, -1, 1],
                 int(np.ceil(len(dates)/6)))[:len(dates)]    

fig, ax = plt.subplots(figsize=(15, 4), constrained_layout=True)
ax.set(title="Даты наступления события")

markerline, stemline, baseline = ax.stem(dates, levels,
                                         linefmt="C3-", basefmt="k-",
                                         use_line_collection=True)

labels = [d.isoformat() for d in dates]
vert = np.array(['top', 'bottom'])[(levels > 0).astype(int)]
for d, l, r, va in zip(dates, levels, labels, vert):
    ax.annotate(r, xy=(d, l), xytext=(-3, np.sign(l)*3),
                textcoords="offset points", va=va, ha="right")

markerline.set_ydata(np.zeros(len(dates)))
plt.setp(markerline, mec="k", mfc="w", zorder=3)

ax.get_xaxis().set_major_locator(mdates.YearLocator())
ax.get_xaxis().set_major_formatter(mdates.DateFormatter("%Y"))
_ = plt.setp(ax.get_xticklabels(), rotation=30, ha="right")

ax.get_yaxis().set_visible(False)
for spine in ["left", "top", "right"]:
    ax.spines[spine].set_visible(False)

ax.margins(y=0.1)
fig.set_facecolor('white')