NumPy Cookbook - Second Edition

Installing IPython and setuptools on Windows: A binary Windows installer for Python 2 or Python 3 is available on the IPython website. Also see http://ipython.org/ipython-doc/stable/install/install.html#windows.

Install setuptools with an installer from http://pypi.python.org/pypi/setuptools#files. Then install pip, like this:

cd C:\Python27\scripts
python .\easy_install-27-script.py pip

Installing IPython on Mac OS X: Install the Apple Developer Tools (Xcode) if necessary. Xcode can be found at https://developer.apple.com/xcode/. Follow the easy_install/pip instructions or the instructions for installation from source provided later in this section.

Installing IPython on Linux: Since there are so many Linux distributions, this section will not be exhaustive:

Installing IPython with easy_install or pip: Install IPython and all the dependencies required for the recipes in this chapter with easy_install using the following command:

$ sudo easy_install ipython pyzmq tornado readline

Alternatively, you can first install pip with easy_install by typing this command in your terminal:

$ sudo easy_install pip

After that, install IPython using pip:

$ sudo pip install ipython pyzmq tornado readline

Installing from source: If you want to use the bleeding-edge development version, then installing from source is for you:

Instructions from the official IPython website at http://ipython.org/install.html

pylab: The pylab switch automatically imports all the SciPy, NumPy, and matplotlib packages. Without this switch, we would have to import these packages ourselves.

All we need to do is enter the following instruction on the command line:

$ ipython --pylab
Type "copyright", "credits" or "license" for more information.

IPython 2.4.1 -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object', use 'object??' for extra details.

Welcome to pylab, a matplotlib-based Python environment [backend: MacOSX].
For more information, type 'help(pylab)'.

In [1]: quit()
quit() or Ctrl + D quits the IPython shell.

Saving a session: We might want to be able to go back to our experiments. In IPython, it is easy to save a session for later use. This is done with the following command:

In [1]: %logstart
Activating auto-logging. Current session state plus future input saved.
Filename       : ipython_log.py
Mode           : rotate
Output logging : False
Raw input log  : False
Timestamping   : False
State          : active

Logging can be switched off using this command:

In [9]: %logoff
Switching logging OFF

Executing a system shell command: You can execute a system shell command in the default IPython profile by prefixing the command with the ! symbol. For instance, the following input will get the current date:

In [1]: !date

In fact, any line prefixed with ! is sent to the system shell. We can also store the command output, as shown here:

In [2]: thedate = !date
In [3]: thedate

Displaying history: We can show the history of commands with the %hist command, like this:

In [1]: a = 2 + 2

In [2]: a
Out[2]: 4

In [3]: %hist
a = 2 + 2
a
%hist

This is a common feature in Command-line Interface (CLI) environments. We can also look up the history with the -g switch:

In [5]: %hist -g a = 2
    1: a = 2 + 2

IPython as a system shell from the official IPython website at http://ipython.org/ipython-doc/dev/interactive/shell.html

Calling the help function: Call the help command. Type a few characters of the function and then press the Tab key (see the following screenshot):

Querying with a question mark: Another option is to put a question mark behind the function name. You will then, of course, need to know the function name, but you don't have to type the help command:

In [3]: arange?

Installing matplotlib on Windows: You can install this with the Enthought distribution, also known as Canopy (http://www.enthought.com/products/epd.php).

It might be necessary to put the msvcp71.dll file in your C:\Windows\system32 directory. You can get it from http://www.dll-files.com/dllindex/dll-files.shtml?msvcp71.

Installing matplotlib on Linux: Let's see how matplotlib can be installed in the various distributions of Linux:

Here is the install command on Debian and Ubuntu:

$ sudo apt-get install python-matplotlib

Installing from source: You can download the latest source from the tar.gz release at Sourceforge (http://sourceforge.net/projects/matplotlib/files/), or from the Git repository using the following command:

$ git clone git://github.com/matplotlib/matplotlib.git

Once it has been downloaded, build and install matplotlib as usual with the following commands:

$ cd matplotlib
$ sudo python setup.py install

Installing matplotlib on Mac OS X: Get the latest DMG file from http://sourceforge.net/projects/matplotlib/files/matplotlib/ and install it. You can also use the Mac Ports, Fink, or Homebrew package managers.

Instructions from the official matplotlib documentation are given at http://matplotlib.org/users/installing.html

Installing the SciPy stack is explained at http://www.scipy.org/install.html

Running a notebook: We can start a notebook with the following command:

$ ipython notebook

[NotebookApp] Using existing profile dir: u'/Users/ivanidris/.ipython/profile_default'
[NotebookApp] The IPython Notebook is running at: http://127.0.0.1:8888
[NotebookApp] Use Control-C to stop this server and shut down all kernels.

As you can see, we are using the default profile. A server started on the local machine at port 8888. You will learn how to configure these settings later on in this chapter. The notebook is opened in your default browser; this is configurable as well (see the following screenshot):

IPython lists all the notebooks in the directory where you started the notebook. In this example, no notebooks were found. The server can be stopped by pressing Ctrl + C.

Running a notebook in the pylab mode: Run a web notebook in the pylab mode with the following command:

$ ipython notebook --pylab

This loads the SciPy, NumPy, and matplotlib modules.

Running a notebook with inline figures: We can display inline matplotlib plots with the inline directive using the following command:

$ ipython notebook --pylab inline

The following steps demonstrate the IPython notebook functionality:

The Installing IPython recipe found in this chapter

Example notebooks at http://nbviewer.ipython.org/github/ipython/ipython/blob/2.x/examples/Notebook/Index.ipynb

Documentation for the sinc() function at http://docs.scipy.org/doc/numpy/reference/generated/numpy.sinc.html

Documentation for the plot() function at http://matplotlib.org/api/pyplot_api.html#matplotlib.pyplot.plot

The Print option: The Print button doesn't actually print the notebook, but allows you to export the notebook as a PDF or HTML document.

Downloading the notebook: Download your notebook to a location chosen by you, using the Download button. We can specify whether we want to download the notebook as a .py file, which is just a normal Python program, or in the JSON format as a .ipynb file. The notebook we created in the previous recipe looks like the following after exporting:

{
 "metadata": {
  "name": "Untitled1"
 }, 
 "nbformat": 2, 
 "worksheets": [
  {
    "cells": [
    {
      "cell_type": "code", 
      "collapsed": false, 
      "input": [
        "plot(sinc(a))"
      ], 
      "language": "python", 
      "outputs": [
      {
        "output_type": "pyout", 
        "prompt_number": 3, 
        "text": [
          "[<matplotlib.lines.Line2D at 0x103d9c690>]"
        ]
      }, 
      {
        "output_type": "display_data", 
        "png": "iVBORw0KGgoAAAANSUhEUgAAAXkAAAD9CAYAAABZVQdHAAAABHNCSVQICAgIf...
          mgkAAAAASUVORK5CYII=\n"
      }
      ], 
      "prompt_number": 3
    }
    ]
  }
  ]
}

Saving the notebook: Save the notebook using the Save button. This will automatically export a notebook in the native JSON format, .ipynb. The file will be stored in the directory where you started IPython initially.

IPython documentation for the passwd() function at http://ipython.org/ipython-doc/2/api/generated/IPython.lib.security.html

OpenSSL documentation at https://www.openssl.org/docs/apps/openssl.html

The SymPy homepage at http://sympy.org/en/index.html