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== strings, unicode and bytes ==

In Python 2 a chain of characters between simple, double or triple quotes creates an ascii string. To create a unicode string one has to use the prefix `u` (which remains valid in Python 3).

In Python 3, a chain of characters between quote will gives rise to a unicode string. To create specifically an ascii string one has to use the prefix `b` (which is already valid in Python 2).

Warning:

Starting from version 9.0, the default distributed version of Sage is using Python 3. See Python3-Switch for more information.

Main caveat

range and xrange

In Python range is a function that returns a list.

Toggle line numbers 
   1 sage-8.9: range(5)
   2 [0, 1, 2, 3, 4]
   3 sage-8.9: type(range(5))
   4 <type 'list'>

In Python 3, range is an object that somehow behave as a list (ie elements can still be acessed with square bracket, it has a length, etc) but it is not a list.

Toggle line numbers 
   1 sage-9.0: range(5)
   2 range(0, 5)
   3 sage-9.0: range(5)[2]
   4 2
   5 sage-9.0: range(5)[1::2]
   6 range(1, 5, 2)
   7 sage-9.0: type(range(5))
   8 <class 'range'>

The iterator xrange is no longer valid in Python 3 simply use range instead.

strings, unicode and bytes

In Python 2 a chain of characters between simple, double or triple quotes creates an ascii string. To create a unicode string one has to use the prefix u (which remains valid in Python 3).

In Python 3, a chain of characters between quote will gives rise to a unicode string. To create specifically an ascii string one has to use the prefix b (which is already valid in Python 2).

Python3-user (last edited 2020-01-02 08:29:00 by chapoton)