You need a reference to an Axes
object to keep drawing on the same subplot.
import matplotlib.pyplot as plt
x = range(100)
y = range(100,200)
fig = plt.figure()
ax1 = fig.add_subplot(111)
ax1.scatter(x[:4], y[:4], s=10, c="b", marker="s", label="first")
ax1.scatter(x[40:],y[40:], s=10, c="r", marker="o", label="second")
plt.legend(loc="upper left")
plt.show()