You can also do this globally via a rcParams dictionary:

import matplotlib.pylab as pylab
params = {'legend.fontsize': 'x-large',
          'figure.figsize': (15, 5),
         'axes.labelsize': 'x-large',
         'axes.titlesize':'x-large',
         'xtick.labelsize':'x-large',
         'ytick.labelsize':'x-large'}
pylab.rcParams.update(params)

If you’re more used to using ax objects to do your plotting, you might find the ax.xaxis.label.set_size() easier to remember, or at least easier to find using tab in an ipython terminal. It seems to need a redraw operation after to see the effect. For example:

import matplotlib.pyplot as plt

# set up a plot with dummy data
fig, ax = plt.subplots()
x = [0, 1, 2]
y = [0, 3, 9]
ax.plot(x,y)

# title and labels, setting initial sizes
fig.suptitle('test title', fontsize=12)
ax.set_xlabel('xlabel', fontsize=10)
ax.set_ylabel('ylabel', fontsize='medium')   # relative to plt.rcParams['font.size']

# setting label sizes after creation
ax.xaxis.label.set_size(20)
plt.draw()

I don’t know of a similar way to set the suptitle size after it’s created.

To only modify the title’s font (and not the font of the axis) I used this:

import matplotlib.pyplot as plt
fig = plt.Figure()
ax = fig.add_subplot(111)
ax.set_title('My Title', fontdict={'fontsize': 8, 'fontweight': 'medium'})

The fontdict accepts all kwargs from matplotlib.text.Text.

An alternative solution to changing the font size is to change the padding. When Python saves your PNG, you can change the layout using the dialogue box that opens. The spacing between the axes, padding if you like can be altered at this stage.

Place right_ax before set_ylabel()

ax.right_ax.set_ylabel('AB scale')

Per the official guide, use of pylab is no longer recommended. matplotlib.pyplot should be used directly instead.

Globally setting font sizes via rcParams should be done with

import matplotlib.pyplot as plt
plt.rcParams['axes.labelsize'] = 16
plt.rcParams['axes.titlesize'] = 16

# or

params = {'axes.labelsize': 16,
          'axes.titlesize': 16}
plt.rcParams.update(params)

# or

import matplotlib as mpl
mpl.rc('axes', labelsize=16, titlesize=16)

# or 

axes = {'labelsize': 16,
        'titlesize': 16}
mpl.rc('axes', **axes)

The defaults can be restored using

plt.rcParams.update(plt.rcParamsDefault)

You can also do this by creating a style sheet in the stylelib directory under the matplotlib configuration directory (you can get your configuration directory from matplotlib.get_configdir()). The style sheet format is

axes.labelsize: 16
axes.titlesize: 16

If you have a style sheet at /path/to/mpl_configdir/stylelib/mystyle.mplstyle then you can use it via

plt.style.use('mystyle')

# or, for a single section

with plt.style.context('mystyle'):
    # ...

You can also create (or modify) a matplotlibrc file which shares the format

axes.labelsize = 16
axes.titlesize = 16

Depending on which matplotlibrc file you modify these changes will be used for only the current working directory, for all working directories which do not have a matplotlibrc file, or for all working directories which do not have a matplotlibrc file and where no other matplotlibrc file has been specified. See this section of the customizing matplotlib page for more details.

A complete list of the rcParams keys can be retrieved via plt.rcParams.keys(), but for adjusting font sizes you have (italics quoted from here)

• axes.labelsize – Fontsize of the x and y labels
• axes.titlesize – Fontsize of the axes title
• figure.titlesize – Size of the figure title (Figure.suptitle())
• xtick.labelsize – Fontsize of the tick labels
• ytick.labelsize – Fontsize of the tick labels
• legend.fontsize – Fontsize for legends (plt.legend(), fig.legend())
• legend.title_fontsize – Fontsize for legend titles, None sets to the same as the default axes. See this answer for usage example.

all of which accept string sizes {'xx-small', 'x-small', 'smaller', 'small', 'medium', 'large', 'larger', 'x-large', 'xxlarge'} or a float in pt. The string sizes are defined relative to the default font size which is specified by

• font.size – the default font size for text, given in pts. 10 pt is the standard value

Additionally, the weight can be specified (though only for the default it appears) by

• font.weight – The default weight of the font used by text.Text. Accepts {100, 200, 300, 400, 500, 600, 700, 800, 900} or 'normal' (400), 'bold' (700), 'lighter', and 'bolder' (relative with respect to current weight).

7 (best solution)

 from numpy import*
 import matplotlib.pyplot as plt
 X = linspace(-pi, pi, 1000)

class Crtaj:

    def nacrtaj(self,x,y):
         self.x=x
         self.y=y
         return plt.plot (x,y,"om")

def oznaci(self):
    return plt.xlabel("x-os"), plt.ylabel("y-os"), plt.grid(b=True)

6 (slightly worse solution)

from numpy import*
M = array([[3,2,3],[1,2,6]])
class AriSred(object):
    def __init__(self,m):
    self.m=m
    
def srednja(self):
    redovi = len(M)
    stupci = len (M[0])
    lista=[]
    a=0
    suma=0
    while a<stupci:
        for i in range (0,redovi):
            suma=suma+ M[i,a]
        lista.append(suma)
        a=a+1
        suma=0
    b=array(lista) 
    b=b/redovi
    return b



OBJ = AriSred(M)
sr = OBJ.srednja()

Others have provided answers for how to change the title size, but as for the axes tick label size, you can also use the set_tick_params method.

E.g., to make the x-axis tick label size small:

ax.xaxis.set_tick_params(labelsize='small')

or, to make the y-axis tick label large:

ax.yaxis.set_tick_params(labelsize='large')

You can also enter the labelsize as a float, or any of the following string options: ‘xx-small’, ‘x-small’, ‘small’, ‘medium’, ‘large’, ‘x-large’, or ‘xx-large’.

libraries

import numpy as np

import matplotlib.pyplot as plt

create dataset

height = [3, 12, 5, 18, 45]

bars = (‘A’, ‘B’, ‘C’, ‘D’, ‘E’)

x_pos = np.arange(len(bars))

Create bars and choose color

plt.bar(x_pos, height, color = (0.5,0.1,0.5,0.6))

Add title and axis names

plt.title(‘My title’)

plt.xlabel(‘categories’)

plt.ylabel(‘values’)

Create names on the x axis

plt.xticks(x_pos, bars)

Show plot

plt.show()

If you aren’t explicitly creating figure and axis objects you can set the title fontsize when you create the title with the fontdict argument.

You can set and the x and y label fontsizes separately when you create the x and y labels with the fontsize argument.

For example:

plt.title('Car Prices are Increasing', fontdict={'fontsize':20})
plt.xlabel('Year', fontsize=18)
plt.ylabel('Price', fontsize=16)

Works with seaborn and pandas plotting (when Matplotlib is the backend), too!