Set Latex greek letter in plotting script using matplotlib

Question

I have a plotting script where I load subtitles (variable subplot_titles) from a JSON file :

example of JSON file :

"subplot_titles" : {

    "0" : "Model: $~w_{0},~w_{a}~$ - flat - optimistic - No $\\gamma$",
    "1" : "Model: $~w_{0},~w_{a}~$ - flat - optimistic - With $\\gamma$",
    "2" : "Model: $~w_{0},~w_{a}~$ - flat - semi-pessimistic - No $\\gamma$",
    "3" : "Model: $~w_{0},~w_{a}~$ - flat - semi-pessimistic - With $\\gamma$"
},

In my script, I load this file like this :

 for i, ax in enumerate(np.ravel(axes)):

    config = load_config('./config.json')

    df = parse_input(config['subplot_files'][i])
    df = format_dataframe(df, config)
    title = config['subplot_titles'][i]
    lgd = plot_barchart(df, ax, title)
    bbea.append(lgd)

But once the figure is generated, I have an uggly symbol "gamma", like this :

I would like to display a Latex gamma symbol.

I tried to add r' in the plotting script to get Latex support :

title = config[r'subplot_titles'][i]

But I get an error.

What can I do to get this gamma greek symbol under Latex displaying ?

Update

The solutions given works but I want to keep the matplotlib font for legend which appears under the form in jSON file :

"bars" : {

    "0" : "$GC_{s}$",
    "1" : "$GC_{ph} + WL$",
    "2" : "$GC_{s} + GC_{ph} + WL$",
    "3" : "$GC_{ph} + WL + XC$",
    "4" : "$GC_{s} + (GC_{ph} + WL + XC)$",
    "5" : "($GC_{s} + GC_{ph} + WL) + XC2$",
    "6" : "$GC_{s} + (GC_{ph} + WL + XC) + XC2$"

},

that produces a nice legend :

For the subplot_titles, I have just to replace a greek symbol by the Latex equivalent but caution, with the real Latex symbol \gamma, not the one which makes part of Latex of matplotlib like the ugly "\gamma" symbol I have shown above, and keep all the rest as it is currently.

I tried to make this subsitution :

title = title.replace("\\gamma", "+r\"\\mathit{\\gamma}")

but without success. How to perform this rendering ?

Answer 1

You can change matplotlib rc settings to use LaTeX, for example by including the following code before you start plotting:

import matplotlib as mpl
mpl.rcParams['text.usetex'] = True

Alternatively, instead of using LaTeX you can just change the font that matplotlib is using to typeset mathematics:

mpl.rcParams['mathtext.fontset'] = 'cm'

'cm' is Computer Modern, the default LaTeX font, but there are also other possibilities.

If you want to fine-tune font selection, LaTeX will be probably a better option. Here is an example:

import matplotlib.pyplot as plt
import matplotlib as mpl

mpl.rcParams['font.family'] = 'sans-serif'
mpl.rcParams['text.usetex'] = True
mpl.rcParams["text.latex.preamble"]  = r"\usepackage{cmbright}"

plt.figure(figsize=(5,3))
plt.title(r"$w_{0},w_{a}$ - flat - optimistic - with $\gamma$")
plt.plot([1, 2], [1, 2], 'r-', label=r"$GC_s$")
plt.plot([1, 2], [3, 1], 'b--', label=r"$GC_{ph} + WL$")
plt.plot([1, 2], [2, 0], 'g-.', label=r"$GC_s + GC_{ph} + WL$")
plt.legend()
plt.show()

Result: