two axes

In gnuplot it is quite easy to create two axes, but I can't figure out
how to do it in matplotlib. I'm trying this:

import matplotlib
matplotlib.use('Agg')
import matplotlib.pyplot as plt

for key1 in keys1:
    ax1.plot(x, y, style, label=label, color=color, linewidth=3)
    ax1.set_xlabel(xlabel)
    ax1.set_ylabel(ylabel1)
    ax2.set_ylabel(ylabel2)
    plt.legend(loc='lower right', shadow=True)
    plt.suptitle(title, fontsize=14, fontweight='bold')
    axes = plt.gca()
    axes.set_ylim([0,1])
    plt.grid(b=True, which='major', color='k', linestyle='--')
    plt.savefig('{}.png'.format(key1), dpi=600)
    plt.close()
    plt.clf()

But I get this error:
lib/python3.3/site-packages/matplotlib/axes.py:4749: UserWarning: No
labeled objects found. Use label='...' kwarg on individual plots.
  warnings.warn("No labeled objects found. "

What am I doing wrong? Thanks.

You didn’t label any of the series that you put on the graph, so the legend has no idea what to call anything thing.

Like the warning (not error) says, use the label parameter on your calls to plot, e.g., ax1.plot(…, label=‘Concentration’) or whatever.

Note though, that you’re mixing up interfaces in your script as written. MPL’s many interfaces are kind of mess, but you seem reasonably familiar with the OO interface, so stick to that. What I mean is once you start messing with ax1, and ax2 directly, don’t revert back to call to plt. As written, you’ll only get a legend on ax2, but you haven’t plotted anything there.

If you want a legend on ax1, use ax1.legend.

-p

···

On Tue, Dec 2, 2014 at 1:59 AM, Tommy Carstensen <tommy.carstensen@…287…> wrote:

In gnuplot it is quite easy to create two axes, but I can’t figure out

how to do it in matplotlib. I’m trying this:

import matplotlib

matplotlib.use(‘Agg’)

import matplotlib.pyplot as plt

for key1 in keys1:

ax1.plot(x, y, style, label=label, color=color, linewidth=3)

ax1.set_xlabel(xlabel)

ax1.set_ylabel(ylabel1)

ax2.set_ylabel(ylabel2)

plt.legend(loc='lower right', shadow=True)

plt.suptitle(title, fontsize=14, fontweight='bold')

axes = plt.gca()

axes.set_ylim([0,1])

plt.grid(b=True, which='major', color='k', linestyle='--')

plt.savefig('{}.png'.format(key1), dpi=600)

plt.close()

plt.clf()

But I get this error:

lib/python3.3/site-packages/matplotlib/axes.py:4749: UserWarning: No

labeled objects found. Use label=’…’ kwarg on individual plots.

warnings.warn("No labeled objects found. "

What am I doing wrong? Thanks.


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