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https://github.com/juliapy/pythonplot.jl

Plotting for Julia based on matplotlib.pyplot
https://github.com/juliapy/pythonplot.jl

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Plotting for Julia based on matplotlib.pyplot

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README 

        
# The PythonPlot module for Julia

[![CI](https://github.com/JuliaPy/PythonPlot.jl/workflows/CI/badge.svg)](https://github.com/JuliaPy/PythonPlot.jl/actions?query=workflow%3ACI)



This module provides a Julia interface to the

[Matplotlib](http://matplotlib.org/) plotting library from Python, and

specifically to the `matplotlib.pyplot` module.



PythonPlot uses the Julia [PythonCall.jl](https://github.com/cjdoris/PythonCall.jl)

package to call Matplotlib directly from Julia with little or no

overhead (arrays are passed without making a copy).  It is based on a fork of the [PyPlot.jl](https://github.com/JuliaPy/PyPlot.jl) package, which uses the older [PyCall.jl](https://github.com/JuliaPy/PyCall.jl) interface to Python, and is intended to function as a mostly drop-in replacement for PyPlot.jl.



This package takes advantage of Julia's [multimedia

I/O](https://docs.julialang.org/en/latest/base/io-network/#Multimedia-I/O-1)

API to display plots in any Julia graphical backend, including as

inline graphics in [IJulia](https://github.com/JuliaLang/IJulia.jl).

Alternatively, you can use a Python-based graphical Matplotlib

backend to support interactive plot zooming etcetera.



## Installation



The PythonPlot package uses the [CondaPkg.jl](https://github.com/cjdoris/CondaPkg.jl) package to automatically install Matplotlib as needed.



(If you configure PythonCall to use some custom Python installation, you will need to install Matplotlib yourself.)



You can either

do inline plotting with [IJulia](https://github.com/JuliaLang/IJulia.jl),

which doesn't require a GUI backend, or use the Qt, wx, or GTK+ backends

of Matplotlib as described below.



## Basic usage



Once Matplotlib and PythonPlot are installed, and you are using a

graphics-capable Julia environment such as IJulia, you can simply type

`using PythonPlot` and begin calling functions in the

[matplotlib.pyplot](http://matplotlib.org/api/pyplot_api.html) API.

For example:



```

using PythonPlot

x = range(0; stop=2*pi, length=1000); y = sin.(3 * x + 4 * cos.(2 * x));

plot(x, y, color="red", linewidth=2.0, linestyle="--")

title("A sinusoidally modulated sinusoid")

```



In general, all of the arguments, including keyword arguments, are

exactly the same as in Python.  (With minor translations, of course,

e.g. Julia uses `true` and `nothing` instead of Python's `True` and

`None`.)



The full `matplotlib.pyplot` API is far too extensive to describe here;

see the [matplotlib.pyplot documentation for more

information](http://matplotlib.org/api/pyplot_api.html).  The Matplotlib

version number is returned by `PythonPlot.version`.



### Differences from PyPlot.jl



Compared to the PyPlot.jl package, there are a few differences in the API.



* To avoid type piracy, the functions `show`, `close`, `step`, and `fill` are renamed to `plotshow`, `plotclose`, `plotstep`, and `plotfill`, respectively.  (You can also access them as `PythonPlot.show` etcetera.)

* The `matplotlib.pyplot` module is exported as `pyplot` rather than as `plt`.

* The PythonCall package performs many fewer automatic conversions from Python types to Julia types (in comparison to PyCall).   If you need to convert Matplotlib return values to native Julia objects, you'll need to do `using PythonCall` and call its `pyconvert(T, o)` or other conversion functions.



### Exported functions



Only the currently documented `matplotlib.pyplot` API is exported.  To use

other functions in the module, you can also call `matplotlib.pyplot.foo(...)`

as `pyplot.foo(...)`.  For example, `pyplot.plot(x, y)` also works.  (And

the raw `Py` object for the `matplotlib` module itself is also accessible

as `PythonPlot.matplotlib`.)



Matplotlib is somewhat inconsistent about capitalization: it has

`contour3D` but `bar3d`, etcetera.  PyPlot renames all such functions

to use a capital *D* (e.g. it has `hist2D`, `bar3D`, and so on).



You must also explicitly qualify some functions

built-in Julia functions.  In particular, `PythonPlot.xcorr`,

`PythonPlot.axes`, and `PythonPlot.isinteractive`

must be used to access `matplotlib.pyplot.xcorr`

etcetera.



If you wish to access *all* of the PyPlot functions exclusively

through `pyplot.somefunction(...)`, as is conventional in Python, you can

do `import PythonPlot as pyplot` instead of `using PythonPlot`.



### Figure objects



You can get the current figure as a `Figure` object (a wrapper

around `matplotlib.pyplot.Figure`) by calling `gcf()`.



The `Figure` type supports Julia's [multimedia I/O

API](https://docs.julialang.org/en/latest/base/io-network/#Multimedia-I/O-1),

so you can use `display(fig)` to show a `fig::PyFigure` and

`show(io, mime, fig)` (or `writemime` in Julia 0.4) to write it to a given `mime` type string

(e.g. `"image/png"` or `"application/pdf"`) that is supported by the

Matplotlib backend.



## Non-interactive plotting



If you use PythonPlot from an interactive Julia prompt, such as the Julia

[command-line prompt](http://docs.julialang.org/en/latest/manual/interacting-with-julia/)

or an IJulia notebook, then plots appear immediately after a plotting

function (`plot` etc.) is evaluated.



However, if you use PythonPlot from a Julia script that is run non-interactively

(e.g. `julia myscript.jl`), then Matplotlib is executed in

[non-interactive mode](http://matplotlib.org/faq/usage_faq.html#what-is-interactive-mode):

a plot window is not opened until you run `plotshow()` (equivalent to `pyplot.show()`

in the Python examples).



## Interactive versus Julia graphics



PythonPlot can use any Julia graphics backend capable of displaying PNG,

SVG, or PDF images, such as the IJulia environment.  To use a

different backend, simply call `pushdisplay` with the desired

`Display`; see the [Julia multimedia display

API](https://docs.julialang.org/en/latest/base/io-network/#Multimedia-I/O-1)

for more detail.



On the other hand, you may wish to use one of the Python Matplotlib

backends to open an interactive window for each plot (for interactive

zooming, panning, etcetera).  You can do this at any time by running:

```

pygui(true)

```

to turn on the Python-based GUI (if possible) for subsequent plots,

while `pygui(false)` will return to the Julia backend.  Even when a

Python GUI is running, you can display the current figure with the

Julia backend by running `display(gcf())`.



If no Julia graphics backend is available when PythonPlot is imported, then

`pygui(true)` is the default.



### Choosing a Python GUI toolkit



Only the [Tk](http://www.tcl.tk/), [wxWidgets](http://www.wxwidgets.org/),

[GTK+](http://www.gtk.org/) (version 2 or 3), and [Qt](http://qt-project.org/) (version 4 or 5; via the PyQt5,

[PyQt4](http://wiki.python.org/moin/PyQt4) or

[PySide](http://qt-project.org/wiki/PySide)), Python GUI backends are

supported by PythonPlot.  (Obviously, you must have installed one of these

toolkits for Python first.)  By default, PythonPlot picks one of these

when it starts up (based on what you have installed), but you can

force a specific toolkit to be chosen by setting the `MPLBACKEND` environment variable

to the desired Python backend *before*

importing PythonPlot:

```

ENV["MPLBACKEND"] = backend

using PythonPlot

```

where `backend` is typically one of `"wxagg"`, `"gtkagg"`, `"gtk3agg"`, `"qt5agg"`, `"qt4agg"`, or `"tkagg"`.

You can

also set a default via the Matplotlib `rcParams['backend']` parameter in your

[matplotlibrc](http://matplotlib.org/users/customizing.html) file.



## Color maps



The PythonPlot module also exports some functions and types based on the

[matplotlib.colors](http://matplotlib.org/api/colors_api.html) and

[matplotlib.cm](http://matplotlib.org/api/cm_api.html) modules to

simplify management of color maps (which are used to assign values to

colors in various plot types).  In particular:



* `ColorMap`: a wrapper around the [matplotlib.colors.Colormap](http://matplotlib.org/api/colors_api.html#matplotlib.colors.Colormap) type.  The following constructors are provided:



  * `ColorMap{T<:Colorant}(name::String, c::AbstractVector{T}, n=256, gamma=1.0)` constructs an `n`-component colormap by [linearly interpolating](http://matplotlib.org/api/colors_api.html#matplotlib.colors.LinearSegmentedColormap) the colors in the array `c` of `Colorant`s (from the [ColorTypes.jl](https://github.com/JuliaGraphics/ColorTypes.jl) package).  If you want a `name` to be constructed automatically, call `ColorMap(c, n=256, gamma=1.0)` instead.  Alternatively, instead of passing an array of colors, you can pass a 3- or 4-column matrix of RGB or RGBA components, respectively (similar to [ListedColorMap](http://matplotlib.org/api/colors_api.html#matplotlib.colors.ListedColormap) in Matplotlib).



  * Even more general color maps may be defined by passing arrays of (x,y0,y1) tuples for the red, green, blue, and (optionally) alpha components, as defined by the [matplotlib.colors.LinearSegmentedColormap](http://matplotlib.org/api/colors_api.html#matplotlib.colors.LinearSegmentedColormap) constructor, via: `ColorMap{T<:Real}(name::String, r::AbstractVector{(T,T,T)}, g::AbstractVector{(T,T,T)}, b::AbstractVector{(T,T,T)}, n=256, gamma=1.0)` or `ColorMap{T<:Real}(name::String, r::AbstractVector{(T,T,T)}, g::AbstractVector{(T,T,T)}, b::AbstractVector{(T,T,T)}, alpha::AbstractVector{(T,T,T)}, n=256, gamma=1.0)`



  * `ColorMap(name::String)` returns an existing (registered) colormap, equivalent to [matplotlib.pyplot.get_cmap](http://matplotlib.org/stable/api/_as_gen/matplotlib.pyplot.get_cmap.html#matplotlib-pyplot-get-cmap)(`name`).



  * `matplotlib.colors.Colormap` objects returned by Python functions are automatically converted to the `ColorMap` type.



* `get_cmap(name::String)` or `get_cmap(name::String, lut::Integer)` call the [matplotlib.pyplot.get_cmap](https://matplotlib.org/stable/api/_as_gen/matplotlib.pyplot.get_cmap.html#matplotlib-pyplot-get-cmap) function.



* `register_cmap(c::ColorMap)` or `register_cmap(name::String, c::ColorMap)` call the [matplotlib.colormaps.register](https://matplotlib.org/stable/api/cm_api.html#matplotlib.cm.ColormapRegistry.register) function.



* `get_cmaps()` returns a `Vector{ColorMap}` of the currently

  registered colormaps.



Note that, given an SVG-supporting display environment like IJulia,

`ColorMap` and `Vector{ColorMap}` objects are displayed graphically;

try `get_cmaps()`!



## 3d Plotting



The PythonPlot package also imports functions from Matplotlib's

[mplot3d](http://matplotlib.org/mpl_toolkits/mplot3d/) toolkit.

Unlike Matplotlib, however, you can create 3d plots directly without

first creating an

[Axes3d](http://matplotlib.org/mpl_toolkits/mplot3d/api.html#axes3d)

object, simply by calling one of: `bar3D`, `contour3D`, `contourf3D`,

`plot3D`, `plot_surface`, `plot_trisurf`, `plot_wireframe`, or

`scatter3D` (as well as `text2D`, `text3D`), exactly like the

correspondingly named methods of

[Axes3d](http://matplotlib.org/mpl_toolkits/mplot3d/api.html#axes3d).

We also export the Matlab-like synonyms `surf` for `plot_surface` (or

`plot_trisurf` for 1d-array arguments) and `mesh` for

`plot_wireframe`.  For example, you can do:

```

surf(rand(30,40))

```

to plot a random 30×40 surface mesh.



You can also explicitly create a subplot with 3d axes via, for

example, `subplot(111, projection="3d")`, exactly as in Matplotlib,

but you must first call the `using3D()` function to ensure that

mplot3d is loaded (this happens automatically for `plot3D` etc.).

The `Axes3D` constructor and the

[art3D](http://matplotlib.org/mpl_toolkits/mplot3d/api.html#art3d)

module are also exported.



## LaTeX plot labels



Matplotlib allows you to [use LaTeX equations in plot

labels](http://matplotlib.org/users/mathtext.html), titles, and so on

simply by enclosing the equations in dollar signs (`$ ... $`) within

the string.  However, typing LaTeX equations in Julia string literals

is awkward because escaping is necessary to prevent Julia from

interpreting the dollar signs and backslashes itself; for example, the

LaTeX equation `$\alpha + \beta$` would be the literal string

`"\$\\alpha + \\beta\$"` in Julia.



To simplify this, PythonPlot uses the [LaTeXStrings package](https://github.com/stevengj/LaTeXStrings.jl) to provide a new `LaTeXString` type that

be constructed via `L"...."` without escaping backslashes or dollar

signs.  For example, one can simply write `L"$\alpha + \beta$"` for the

abovementioned equation, and thus you can do things like:

```

title(L"Plot of $\Gamma_3(x)$")

```

If your string contains *only* equations, you can omit the dollar

signs, e.g. `L"\alpha + \beta"`, and they will be added automatically.

As an added benefit, a `LaTeXString` is automatically displayed as a

rendered equation in IJulia.  See the LaTeXStrings package for more

information.



## SVG output in IJulia



By default, plots in IJulia are sent to the notebook as PNG images.

Optionally, you can tell PythonPlot to display plots in the browser as

[SVG](https://en.wikipedia.org/wiki/Scalable_Vector_Graphics) images,

which have the advantage of being resolution-independent (so that they

display without pixellation at high-resolutions, for example if you

convert an IJulia notebook to PDF), by running:

```

PythonPlot.svg(true)

```

This is not the default because SVG plots in the browser are much

slower to display (especially for complex plots) and may display

inaccurately in some browsers with buggy SVG support.  The `PythonPlot.svg()`

method returns whether SVG display is currently enabled.



Note that this is entirely separate from manually exporting plots to SVG

or any other format.  Regardless of whether PythonPlot uses SVG for

browser display, you can export a plot to SVG at any time by using the

Matplotlib

[savefig](http://matplotlib.org/api/pyplot_api.html#matplotlib.pyplot.savefig)

command, e.g. `savefig("plot.svg")`.



## Modifying matplotlib.rcParams

You can mutate the `rcParams` dictionary that Matplotlib uses for global parameters following this example:

```jl

PythonPlot.matplotlib.rcParams["font.size"] = 15

```



## Author



This module was written by [Steven G. Johnson](http://math.mit.edu/~stevenj/).