Variable names

Allowed names for identifier (name of variable or function):

Any sequence of alphabetical character, number, or underline character _
First symbol has to be a character
Case sensitive
Not a python built-in keyword

Name space

The Python interpreter maps the name of an identifier in the active name space. The active name space depends on the active code block (module, function). The identifier can be local or global with respect to the active code block.

   1 def bad_style(x):
   2         # Name space of bad_style
   3         global y
   4         y=x 
   5         z=x
   6         return x
   7 
   8 # Name space of __main__
   9 x,y,z=2,2,2
  10 x=bad_style(1)
  11 print 'x=',x,'y=',y,'z=',z
  12 # y is changed!

   1 import scipy
   2 scipy.pi # pi is in the name space of scipy
   3 
   4 from scipy import pi
   5 pi # pi is in the active name space
   6 
   7 from scipy import *
   8 pi # all identifiers of scipy are in the active name space
   9 
  10 del(pi) # Deletes pi from the active name space
  11 reset   # ipython function to delete all identifiers

Built-in

Scalar

Plain integer: 9
Long integer: 9**99, 1L
Hex integer: 0x10
Floating point: 0.1
Exponential floating point: 1e-3
Complex: 3+2j

Casting

int()
long()
float()
complex()
str()

Sequences

String

   1 s1='Hello world'
   2 s2="Hello world"
   3 s1==s2
   4 
   5 s='"'
   6 s="'"

Dictionary

   1 D={1:'one',2:'two','one':1,'two':2}
   2 D['one']
   3 D[1]

Extended data types

Array

NumPy/SciPy provides a multidimensional array data type. An array can hold arbitrary Python objects but usually they are used for N-dimensional numeric data types.

Array creation

empty((d1,d2),dtype) returns uninitialized array of shape d1,d2.
zeros((d1,d2),dtype) returns array of shape d1,d2 filled with zeros
ones((d1,d2),dtype) returns array of shape d1,d2 filled with ones
array(object,dtype) returns an array from an object, e.g. a list
dtype fundamental C data type e.g. uint8, int16, int64, float32, float64

Array indexing

A[y,x] returns (y,x) element of the array
A[:,x] returns all elements of the y-dimension at x
A[y1:y2,x]
A[:,:] returns a copy of two dimensional array A
A[:,:,0] returns the first sub-image of a 3-dimensional array

LehreWiki: SiaProgrammingPythonDatatypes (last edited 2008-04-13 17:13:34 by anonymous)

-  ⇤ ← Revision 5 as of 2008-04-13 12:38:36 → 
  Size: 1633
  Editor: anonymous
  Comment:
+   ← Revision 6 as of 2008-04-13 17:13:34 → ⇥
  Size: 2615
  Editor: anonymous
  Comment:
-Deletions are marked like this.
+Additions are marked like this.
 Line 67:
+{{{#!python
s1='Hello world'
s2="Hello world"
s1==s2
-Line 68:
+Line 72:
-=== Tuple ===

=== List ===
+s='"'
s="'"
}}}
-Line 73:
+Line 76:
+{{{#!python
D={1:'one',2:'two','one':1,'two':2}
D['one']
D[1]
}}}
-Line 78:
+Line 86:
-= Copy and reference =
+NumPy/SciPy provides a multidimensional '''array''' data type. An array can hold arbitrary Python objects but usually they are used for N-dimensional numeric data types.

=== Array creation ===

 * {{{empty((d1,d2),dtype)}}} returns uninitialized array of shape d1,d2. 
 * {{{zeros((d1,d2),dtype)}}} returns array of shape d1,d2 filled with zeros
 * {{{ones((d1,d2),dtype)}}} returns array of shape d1,d2 filled with ones
 * {{{array(object,dtype)}}} returns an array from an object, e.g. a list
 * {{{dtype}}} fundamental C data type e.g. uint8, int16, int64, float32, float64

=== Array indexing ===

 * {{{A[y,x]}}} returns (y,x) element of the array
 * {{{A[:,x]}}} returns all elements of the y-dimension at x
 * {{{A[y1:y2,x]}}} 
 * {{{A[:,:]}}} returns a copy of two dimensional array A 
 * {{{A[:,:,0]}}} returns the first sub-image of a 3-dimensional array