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IPython and Shell Commands

IPython and Shell Commands

Shell Commands in IPython

Any command that works at the command-line can be used in IPython by prefixing it with the ! character.

Example

! echo 'hello world!' # echo is like Python's print function

hello world!

! pwd # = print working dir

/tmp
For Unix shell, more see: The Unix Shell

Passing Values to and from the Shell

Shell commands can not only be called from IPython, but can also be made to interact with the IPython namespace. For example, we can save the output of any shell command to a Python list using the assignment operator.

For example

contents = !ls
contents

['my-project']

directory = !pwd

directory

Note that these results are not returned as lists, but as a special shell return type defined in IPython:

type(directory)

IPython.utils.text.SList

This looks and acts a lot like a Python list, but has additional functionality, such as the grep and fields methods and the s, n, and p properties that allow us to search, filter, and display the results in convenient ways.

Communication in the other direction–passing Python variables into the shell–is possible using the {varname} syntax:

name = 'Ben'
! echo "hello {name}"

hello Ben

Shell commands in the notebook are executed in a temporary subshell. If we’d like to execute the shell commands in a more enduring way, we can use the % magic command.

With %automagic magic function, we can enable automagic function. Then available shell-like magic functions, such as %cd , %cat, %cp, %env, %ls, %man, %mkdir, %more, %mv, %pwd, %rm, and %rmdir, can be used without the % sign.

Magic Commands

There are two types of magic commands

  • Line magics: start with %
  • Cell magics: start with %%

Useful magic commands:

  • %matplotlib: activates matplotlib interactive support during an IPython session
  • %run: runs a Python script from within IPython shell
  • %time: displays time required by IPython environment to execute a Python expression.
  • %timeit: uses the Python timeit module which runs a statement 100,000 times (by default) and then provides the mean of the fastest three times.
  • %%writefile: Write the contents of the cell to a file. The file will be overwritten unless the -a (–append) flag is specified.

Reference