You can directly specify the dashes length/space using the dashes=(length, interval space) argument inside the plot command.
import matplotlib.pyplot as plt
fig,ax = plt.subplots()
ax.plot([0, 1], [0, 1], linestyle="--", dashes=(5, 1)) #length of 5, space of 1
ax.plot([0, 1], [0, 2], linestyle="--", dashes=(5, 5)) #length of 5, space of 5
ax.plot([0, 1], [0, 3], linestyle="--", dashes=(5, 10)) #length of 5, space of 10
ax.plot([0, 1], [0, 4], linestyle="--", dashes=(5, 20)) #length of 5, space of 20
