[IPython-user] Using argparse to implement %magics

[Robert Kern]

argparse is my command-line option parser of choice these days, and I always 
thought it would be a nice way to implement some of the IPython %magics that 
have such options. I recently had the occasion to write some of my own %magics, 
so I tried it out. Here are the results:


In [1]: text = 'Foo!'

In [2]: %fwrite?
Type:           Magic function
Base Class:     <type 'instancemethod'>
Namespace:      IPython internal
File:           /Users/rkern/.ipython/mymagics.py
Definition:     %fwrite(self, arg)
Docstring:
     Write text out to a file.

     %fwrite [-e ENCODING] [-m MODE] variable [filename]

     positional arguments:
       variable              the name of the variable
       filename              the filename to write [default: the variable's name]

     optional arguments:
       -e ENCODING, --encoding ENCODING
                             the encoding to use for unicode objects; no effect on
                             str objects [default: utf-8]
       -m MODE, --mode MODE  the file mode to use when opening the file for writing


In [3]: %fwrite text somefile.txt

In [4]: !cat somefile.txt
IPython system call: cat somefile.txt
Foo!
In [5]: %fread?
Type:           Magic function
Base Class:     <type 'instancemethod'>
Namespace:      IPython internal
File:           /Users/rkern/.ipython/mymagics.py
Definition:     %fread(self, arg)
Docstring:
     Read text from a file into a variable.

     %fread [-e ENCODING] [-m MODE] variable filename

     positional arguments:
       variable              the name of the variable
       filename              the filename to read from

     optional arguments:
       -e ENCODING, --encoding ENCODING
                             decode the text using this encoding [default: do not
                             attempt to decode]
       -m MODE, --mode MODE  the file mode to use when opening the file for reading


In [7]: %fread x somefile.txt

In [8]: x
Out[8]: 'Foo!'

In [9]: %sym?
Type:           Magic function
Base Class:     <type 'instancemethod'>
Namespace:      IPython internal
File:           /Users/rkern/.ipython/mymagics.py
Definition:     %sym(self, arg)
Docstring:
     Create Sympy variables easily.

     %sym [-r] [-i] [-c] [-f] [-q] names [names ...]

     positional arguments:
       names           the names of the variables to create

     optional arguments:
       -r, --real      symbols are real variables
       -i, --int       symbols are integer variables
       -c, --complex   symbols are complex variables
       -f, --function  symbols are functions
       -q, --quiet     do not print out verbose information


In [10]: %sym x y z
Adding variables:
   x
   y
   z

In [13]: x+y
Out[13]: x + y

In [14]: %sym -c z
Adding complex variables:
   z

In [15]: z.is_complex
Out[15]: True

In [17]: %sym -i i j k
Adding integer variables:
   i
   j
   k

In [18]: i.is_integer
Out[18]: True

In [20]: %sym -f f g h
Adding function variables:
   f
   g
   h

In [25]: type(f)
Out[25]: <class 'sympy.core.function.FunctionClass'>


-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco
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