Main caveat

1. print

In Python 2, print is a keyword (as for, if, etc)

   1 sage-8.9: print "hello", 1, 2
   2 hello 1 2

In Python 3, print becomes a function {{{#highlight python sage-9.0: print("hello", 1, 2) hello 1 2 }}} Writing a print statement without the parenthesis will result in a SyntaxError {{{#highlight python sage: print "hello", 1, 2

• File "<ipython-input-9-e91077222f2e>", line 1

  • print "hello", Integer(1), Integer(2)
    • ^

SyntaxError: invalid syntax }}}

2. range and xrange

In Python range is a function that returns a list.

   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.

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The iterator xrange is no longer valid in Python 3 simply use range instead.

3. 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).