Book Image

NumPy Cookbook

Book Image

NumPy Cookbook

Overview of this book

Today's world of science and technology is all about speed and flexibility. When it comes to scientific computing, NumPy is on the top of the list. NumPy will give you both speed and high productivity. "NumPy Cookbook" will teach you all about NumPy, a leading scientific computing library. NumPy replaces a lot of the functionality of Matlab and Mathematica, but in contrast to those products, it is free and open source. "Numpy Cookbook" will teach you to write readable, efficient, and fast code that is as close to the language of Mathematics as much as possible with the cutting edge open source NumPy software library. You will learn about installing and using NumPy and related concepts. At the end of the book, we will explore related scientific computing projects. This book will give you a solid foundation in NumPy arrays and universal functions. You will also learn about plotting with Matplotlib and the related SciPy project through examples. "NumPy Cookbook" will help you to be productive with NumPy and write clean and fast code.
Table of Contents (17 chapters)
NumPy Cookbook
Credits
About the Author
About the Reviewers
www.PacktPub.com
Preface
Index

Using IPython as a shell


Scientists and engineers are used to experimenting. IPython was created by scientists with experimentation in mind. The interactive environment that IPython provides is viewed by many as a direct answer to Matlab, Mathematica, and Maple and R.

Following is a list of features of the IPython shell:

  • Tab completion

  • History mechanism

  • Inline editing

  • Ability to call external Python scripts with %run

  • Access to system commands

  • The pylab switch

  • Access to Python debugger and profiler

How to do it...

This section describes how to use the IPython shell.

  • The pylab switch: 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 0.12 -- 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, 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 as follows:

    In [9]: %logoff
    Switching logging OFF
    
  • Executing system shell commands: Execute system shell commands 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. Also, we can 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 () for example:

    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 search through the history with the -g switch

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

Note

Downloading the example code

You can download the example code files for all Packt books you have purchased from your account at http://www.packtpub.com. If you purchased this book elsewhere, you can visit http://www.packtpub.com/support and register to have the files e-mailed directly to you.

How it works...

We saw a number of so called "magic functions" in action. These functions start with the % character. If the magic function is used on a line by itself, the % prefix is optional.