How to autoscale y axis in matplotlib? [duplicate]

Question

I'm currently creating many plots and some look great while other need some adjustment. From below how can I make the hard to see plot line easier to see without having to manually plot them? I plot 50-100 of these at a time then add them to a pdf report. I'd like to add space under the line, for example have ylim min limit set to -0.1, but do it automatically.

This one is hard to see plot line:

This one is easy to see plot line:

Here is my code for plotting:

def plot(chan_data):
'''Uses matplotlib to plot a channel
'''
f, ax = plt.subplots(1, figsize=(8, 2.5))
x = dffinal['time'].keys()    
ax.plot(x, dffinal[chan_data].values, linewidth=0.4, color='blue')
ax.xaxis.set_major_formatter(mdates.DateFormatter('%m/%d/%Y - %H:%M'))
ax.xaxis.set_major_locator(mdates.AutoDateLocator(interval_multiples=True))

lgd1 = ax.legend(loc='center left', bbox_to_anchor=(1, 0.5))

f.autofmt_xdate()
ax.set_ylabel(dffinal[chan_data].name)
ax.grid('on')

#I've tried these with no luck
#ax.autoscale(enable=True, axis='y', tight=False)
#ax.set_ymargin(0.5)
#ax.set_autoscaley_on(True)

fname = ".\\plots\\" + chan_data + ".png"
print "Creating: " + fname
plt.savefig(fname, dpi=100, bbox_extra_artist=(lgd1,), bbox_inches='tight')
plt.close()
return fname    

Answer 1

You want margins doc

ex

ax.margins(y=.1)

Also see Add margin when plots run against the edge of the graph