Change y range to start from 0 with matplotlib

Try this

import matplotlib.pyplot as plt
xdata = [1, 4, 8]
ydata = [10, 20, 30]
plt.plot(xdata, ydata)
plt.ylim(ymin=0)  # this line
plt.show()

doc string as following:

>>> help(plt.ylim)
Help on function ylim in module matplotlib.pyplot:

ylim(*args, **kwargs)
    Get or set the *y*-limits of the current axes.

    ::

      ymin, ymax = ylim()   # return the current ylim
      ylim( (ymin, ymax) )  # set the ylim to ymin, ymax
      ylim( ymin, ymax )    # set the ylim to ymin, ymax

    If you do not specify args, you can pass the *ymin* and *ymax* as
    kwargs, e.g.::

      ylim(ymax=3) # adjust the max leaving min unchanged
      ylim(ymin=1) # adjust the min leaving max unchanged

    Setting limits turns autoscaling off for the y-axis.

    The new axis limits are returned as a length 2 tuple.

The range must be set after the plot.

import matplotlib.pyplot as plt
f, ax = plt.subplots(1)
xdata = [1, 4, 8]
ydata = [10, 20, 30]
ax.plot(xdata, ydata)
ax.set_ylim(ymin=0)
plt.show(f)

If ymin is changed before plotting, this will result in a range of [0, 1].

Edit: the ymin argument has been replaced by bottom:

ax.set_ylim(bottom=0)

Documentation: https://matplotlib.org/stable/api/_as_gen/matplotlib.axes.Axes.set_ylim.html

You can do the same on the x axis with left and right:

ax.set_xlim(left=0)

Documentation: https://matplotlib.org/stable/api/_as_gen/matplotlib.axes.Axes.set_xlim.html