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Introduction

This document describes PyChart Version 1.25. PyChart is a Python library for creating "professional" quality charts. It produces line plots, bar plots, range-fill plots, and pie charts in Postscript, PDF, PNG, or SVG. The following sections illustrate some uses of Pychart.

Line plot

linetest.png

This example draws a simple line plot. Below is the source code needed to produce this chart.

linetest.py: 

# This line imports all the chart modules.
from pychart import *
theme.get_options()

# We have 10 sample points total.  The first value in each tuple is
# the X value, and subsequent values are Y values for different lines.
data = [(10, 20, 30), (20, 65, 33),
        (30, 55, 30), (40, 45, 51),
        (50, 25, 27), (60, 75, 30),
        (70, 80, 42), (80, 62, 32),
        (90, 42, 39), (100, 32, 39)]

# The format attribute speficies the text to be drawn at each tick mark.
# Here, texts are rotated -60 degrees ("/a-60"), left-aligned ("/hL"),
# and numbers are printed as integers ("%d").
xaxis = axis.X(format="/a-60/hL%d", tic_interval = 20, label="Stuff")
yaxis = axis.Y(tic_interval = 20, label="Value")

# Define the drawing area. "y_range=(0,None)" tells that the Y minimum
# is 0, but the Y maximum is to be computed automatically. Without
# y_ranges, Pychart will pick the minimum Y value among the samples,
# i.e., 20, as the base value of Y axis.
ar = area.T(x_axis=xaxis, y_axis=yaxis, y_range=(0,None))

# The first plot extracts Y values from the 2nd column
# ("ycol=1") of DATA ("data=data"). X values are takes from the first
# column, which is the default.
plot = line_plot.T(label="foo", data=data, ycol=1, tick_mark=tick_mark.star)
plot2 = line_plot.T(label="bar", data=data, ycol=2, tick_mark=tick_mark.square)

ar.add_plot(plot, plot2)

# The call to ar.draw() usually comes at the end of a program.  It
# draws the axes, the plots, and the legend (if any).

ar.draw()

To produce a Postscript chart, just feed the file to Python. 

% python linetest.py >linetest.eps

Or, to produce a PDF chart, run python like below 1: 

% python linetest.py --format=pdf >linetest.pdf

PyChart also supports PNG, SVG, and interactive X11 display. For more information about output control, Options.

Every pychart program starts with from pychart import * to import classes and objects provided by PyChart. Each chart is represented by an area object, which defines the size , the coordinate system (linear, log, etc), and plots to be drawn in the chart. The final line of the program should end with area.draw(), which draws all the components of the chart to the standard output.

Bar plot

bartestv.png

Above example is a little more complicated chart. the below program generates this chart. 

from pychart import *
theme.get_options()

data = [(10, 20, 30, 5), (20, 65, 33, 5), (30, 55, 30, 5), (40, 45, 51, 7),
        (50, 25, 27, 3), (60, 75, 30, 5), (70, 80, 42, 5), (80, 62, 32, 5),
        (90, 42, 39, 5), (100, 32, 39, 4)]

# The attribute y_coord_system="category" tells that the Y axis values
# should be taken from samples, y_category_col'th column of
# y_category_data.  Thus, in this example, Y values will be
# [40,50,60,70,80].
ar = area.T(y_coord = category_coord.T(data[3:8], 0),
            x_grid_style=line_style.gray50_dash1,
            x_grid_interval=20,
            x_range = (0,100),
            x_axis=axis.X(label="X label"),
            y_axis=axis.Y(label="Y label"),
            bg_style = fill_style.gray90,
            border_line_style = line_style.default)

# Below call sets the default attributes for all bar plots.
chart_object.set_defaults(bar_plot.T, direction="horizontal", data=data)

ar.add_plot(bar_plot.T(label="foo", cluster=(0,3)))
ar.add_plot(bar_plot.T(label="bar", hcol=2, cluster=(1,3)))
ar.add_plot(bar_plot.T(label="baz", hcol=3, cluster=(2,3)))
ar.draw()

Footnotes

  1. To handle command-line options such as --format=pdf, you need to put theme.get_options() in the beginning of your file. See Options.