symrange Module

class srange.symrange.symrange(endVal, negativeFirst=False, auto_reset=True)

symrange class.

This class provides functions to loop symmetrically outward from 0 i.e., 0,1,-1,2,-2,3,-3,... endVal can only be a positive integer or 0

EXAMPLE::

>>> for i in symrange(2): print i
prints:
0 1 -1 2 -2 3 -3

>>> for i in symrange(2,True): print i
prints:
0 -1 1 -2 2 -3 3

NOTE:

symrange can only contain integers.

variables and methods that you may be interested in:

variables
self.endVal	the highest value +/- returned, this is always >= 0
self.negativeFirst	if True then 0,-1,+1,-2,+2,... Otherwise 0,+1,-1,+2,-2,...
self.auto_reset	if True (default), then previous is reset to None at each call to __iter__
self.length	total number of items in range, you can also get this from len(symrange(n)) or symrange(n).len()
self.previous	last value returned by the iterator, when previous==None, then a call to next() returns 0

methods
next()	returns next value, updates previous too
last()	returns the last number in the range, for self.r=”3,5,9-20”, self.last() returns 20
len()	returns number of points in the range, for self.r=”3,5,9-20”, self.len() returns 14
first()	returns first value of iteration, always returns 0
after(prev)	returns value that follows prev, without changing the current point in iteration
index(ipnt)	return the ipntth number from range, first number is ipnt==0, returns None if ipnt negative or too big, same as symrange(2)[ipnt]
val2index(m)	returns index into range that corresponds to m. e.g. for r=‘0,-1,1,-2,2’, m=1 returns 2.
list(self)	returns a list where each element is a value in the range, CAUTION this can make a VERY big list if n is large

special methods	command	result using: syr = symrange(5)
__getitem__(n)	print syr[3]	2
__len__()	print len(syr)	11
__str__()	print str(syr)	symrange starting from 0, going to 5, doing positives first, current value = “initialized to start”
__repr__()	print repr(syr)	symrange[endVal=5, negativeFirst=False, previous=None, len=11, auto_reset=True]

after(val)

Return the value of the element that follows after val (which is given).

first()

Return the value of the first item in the range. This is just for completeness, it always returns 0

index(n)

Returns the n-th element from the range, zero based, n==0 is first element. This method uses but does not change any internal variables, e.g. no self.xxxx This functionality also available by symrange(2)[n], which calles __getitem__() below

last()

Return the value of the last item in the range. This method uses but does not change any internal variables, e.g. no self.xxxx

len()

Return the number of items in the symrange. Usage: as symrange(3).len()

list()

Expands the symrange into a standard python list. This method uses but does not change any internal variables, e.g. no self.xxxx

EXAMPLE::

>>> print symrange(2).list()
[0, 1, -1, 2, -2]

CAUTION:

The following statement:

>>> symrange(100000).list()

will produce a list with 200001 elements!

Max list length for a 32 bit system is (2^32 - 1)/2/4 = 536870912 on my computer I get a MemoryError for lengths > 1e8, so limit to 1e7

next()

Return the next value in the symrange.

val2index(val)

Return the index into the symrange that produces val. This method uses but does not change any internal variables, e.g. no self.xxxx

EXAMPLE::

>>> sr = symrange(4)
>>> print sr.val2index(3)
5