#acl AdminGroup:read,write EditorGroup:read All:read
#format wiki
#language en
#pragma section-numbers off

= Functions =

== Function with one argument ==
{{{
In [124]: def quadrat(x):
   .....:     return x**2
   .....:

In [125]: quadrat(2)
Out[125]: 4
}}}

== Function with variable number of arguments ==
{{{
In [126]: def printargs(*args):
   .....:     for arg in args:
   .....:         print arg
   .....:

In [127]: printargs(a)
[1, 2, 3]

In [128]: printargs(a,range(4))
[1, 2, 3]
[0, 1, 2, 3]
}}}
== Function with variable number of keywords ==

{{{
In [131]: def printkeys(**kw):
   .....:     for k in kw.keys():
   .....:         print k,kw[k]
   .....:

In [132]: printkeys(key1=10,key2='Hallo')
key2 Hallo
key1 10
}}}


== Function with functions as arguments ==

Functions can be passed to functions as arguments. 

{{{#!python
from scipy import sin,pi

def func(x,f):
	return f(x)

print func(pi/2,sin)
}}}

=== eval(), apply() ===

In Matlab or IDL the passing of functions to functions works only with a detour using {{{feval()}}} or {{{Call_function()}}}

 * [[http://groups.google.com/group/comp.lang.idl-pvwave/browse_thread/thread/acf94d8f621caf95/47decec322cf5094?q=function+parameters&rnum=4|IDL passing functions to functions]]
 
Of course, this way is possible in Python as well using the {{{eval()}}} or {{{apply()}}} function. 

{{{#!python
apply(sin,(pi/2,))

f='sin'
x=pi/2.0
eval(f+'('+str(x)+')')
}}}

= Lambda expressions =

Lambda expressions are (anonymous) one line functions
{{{#!python

l=lambda x: x**2-1
l(4)
}}}

= Mapping =

Similar as {{{apply()}}} works with one argument one can call {{{map()}}} with a sequence

{{{#!python
map(len,['Always','look','on','the','bright','side','of','life'])
[6, 4, 2, 3, 6, 4, 2, 4]
}}}

The following example shows the combined usage of a lambda expression
{{{#!python
map(lambda s:len(s)+1,['Always','look','on','the','bright','side','of','life'])
[7, 5, 3, 4, 7, 5, 3, 5]
}}}