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.

   1 from scipy import sin,pi
   2 
   3 def func(x,f):
   4         return f(x)
   5 
   6 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()

• IDL passing functions to functions

Of course, this way is possible in Python as well using the eval() or apply() function.

   1 apply(sin,(pi/2,))
   2 
   3 f='sin'
   4 x=pi/2.0
   5 eval(f+'('+str(x)+')')

Lambda expressions

Lambda expressions are (anonymous) one line functions

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

Mapping

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

   1 map(len,['Always','look','on','the','bright','side','of','life'])
   2 [6, 4, 2, 3, 6, 4, 2, 4]

The following example shows the combined usage of a lambda expression

   1 map(lambda s:len(s)+1,['Always','look','on','the','bright','side','of','life'])
   2 [7, 5, 3, 4, 7, 5, 3, 5]