Drawing a Cartesian coordinate system in python

Again one of these things that maybe 100 other people will ever need to do in their lives. In case you are one of us though here is a short convenient Python class that will make your life easier 😀

import numpy as np
import matplotlib.pyplot as plt
from mpl_toolkits.axisartist import SubplotZero

class Axes():
    
    def __init__(self, xlim=(-5,5), ylim=(-5,5), figsize=(12,5)):
        self.xlim = xlim
        self.ylim = ylim
        self.figsize  = figsize
        self.__scale_arrows__()

    def __drawArrow__(self, x, y, dx, dy, width, length):
        plt.arrow(
            x, y, dx, dy, 
            color       = 'k',
            clip_on     = False, 
            head_width  = self.head_width, 
            head_length = self.head_length
        ) 
        
    def __scale_arrows__(self):
        """ Make the arrows look good regardless of the axis limits """
        xrange = self.xlim[1] - self.xlim[0]
        yrange = self.ylim[1] - self.ylim[0]
        
        self.head_width  = min(xrange/30, 0.25)
        self.head_length = min(yrange/30, 0.3)
        
    def __drawAxis__(self):
        """
        Draws the 2D cartesian axis
        """
        # A subplot with two additional axis, "xzero" and "yzero"
        # corresponding to the cartesian axis
        ax = SubplotZero(self.fig, 1, 1, 1)
        self.fig.add_subplot(ax)
        
        # make xzero axis (horizontal axis line through y=0) visible.
        for axis in ["xzero","yzero"]:
            ax.axis[axis].set_visible(True)
        # make the other axis (left, bottom, top, right) invisible
        for n in ["left", "right", "bottom", "top"]:
            ax.axis[n].set_visible(False)
            
        # Plot limits
        plt.xlim(self.xlim)
        plt.ylim(self.ylim)

        # Draw the arrows
        self.__drawArrow__(self.xlim[1], 0, 0.01, 0, 0.3, 0.2) # x-axis arrow
        self.__drawArrow__(0, self.ylim[1], 0, 0.01, 0.2, 0.3) # y-axis arrow
        
        
    def draw(self):
        # First draw the axis
        self.fig = plt.figure(figsize=self.figsize)
        self.__drawAxis__()



#--------------------------------------------------------
# Main Code
#--------------------------------------------------------
axes = Axes(xlim=(-5,5), ylim=(-5,5), figsize=(9,7))
axes.draw()

Which produces

It is also very easy to change the axis limits

# Create the cartesian axis
axes = Axes(xlim=(0,10), ylim=(-5,5), figsize=(9,7))
axes.draw()