如何为上限设置“自动”，但通过matplotlib.pyplot保持固定的下限

I want to set the upper limit of the y-axis to ‘auto’, but I want to keep the lower limit of the y-axis to always be zero. I tried ‘auto’ and ‘autorange’, but those don’t seem to work. Thank you in advance.

Here is my code:

import matplotlib.pyplot as plt

def plot(results_plt,title,filename):

    ############################
    # Plot results

    # mirror result table such that each parameter forms an own data array
    plt.cla()
    #print results_plt
    XY_results = []

    XY_results = zip( *results_plt)

    plt.plot(XY_results[0], XY_results[2], marker = ".")

    plt.title('%s' % (title) )
    plt.xlabel('Input Voltage [V]')
    plt.ylabel('Input Current [mA]')

    plt.grid(True)
    plt.xlim(3.0, 4.2)  #***I want to keep these values fixed"
    plt.ylim([0, 80]) #****CHANGE**** I want to change '80' to auto, but still keep 0 as the lower limit 
    plt.savefig(path+filename+'.png')

You can pass just left or right to set_xlim:

plt.gca().set_xlim(left=0)

For the y axis, use bottom or top:

plt.gca().set_ylim(bottom=0)

Just set xlim for one of the limits:

plt.xlim(xmin=0)

As aforementioned and according to the matplotlib documentation, the x-limits of a given axis ax can be set using the set_xlim method of the matplotlib.axes.Axes class.

For instance,

>>> ax.set_xlim(left_limit, right_limit)
>>> ax.set_xlim((left_limit, right_limit))
>>> ax.set_xlim(left=left_limit, right=right_limit)

One limit may be left unchanged (e.g. the left limit):

>>> ax.set_xlim((None, right_limit))
>>> ax.set_xlim(None, right_limit)
>>> ax.set_xlim(left=None, right=right_limit)
>>> ax.set_xlim(right=right_limit)

To set the x-limits of the current axis, the matplotlib.pyplot module contains the xlim function that just wraps matplotlib.pyplot.gca and matplotlib.axes.Axes.set_xlim.

def xlim(*args, **kwargs):
    ax = gca()
    if not args and not kwargs:
        return ax.get_xlim()
    ret = ax.set_xlim(*args, **kwargs)
    return ret

Similarly, for the y-limits, use matplotlib.axes.Axes.set_ylim or matplotlib.pyplot.ylim. The keyword arguments are top and bottom.

Just add a point on @silvio ‘s: if you use axis to plot like figure, ax1 = plt.subplots(1,2,1). Then ax1.set_xlim(xmin = 0) also works!