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What are major differences between Python 2 and Python 3?

asked Nov 26, 2015 by learner

1 Answer

Python 2′s print statement has been replaced by the print() function, meaning that we have to wrap the object that we want to print in parentheses. Python 2 doesn’t have a problem with additional parentheses, but in contrast, Python 3 would raise a SyntaxError if we called the print function the Python 2-way without the Parenthesis.

This change is particularly dangerous if you are porting code, or if you are executing Python 3 code in Python 2, since the change in integer-division behavior can often go unnoticed (it doesn’t raise a SyntaxError).\ So, I still tend to use a float(3)/2 or 3/2.0 instead of a 3/2 in my Python 3 scripts to save the Python 2 guys some trouble (and vice versa, I recommend a from __future__ import division in your Python 2 scripts).


Python 2 has ASCII str() types, separate unicode(), but no byte type.Now, in Python 3, we finally have Unicode (utf-8) strings, and 2 byte classes: byte and bytearrays.

The usage of xrange() is very popular in Python 2.x for creating an iterable object, e.g., in a for-loop or list/set-dictionary-comprehension.\ The behavior was quite similar to a generator (i.e., “lazy evaluation”), but here the xrange-iterable is not exhaustible – meaning, you could iterate over it infinitely.

Thanks to its “lazy-evaluation”, the advantage of the regular range() is that xrange() is generally faster if you have to iterate over it only once (e.g., in a for-loop). However, in contrast to 1-time iterations, it is not recommended if you repeat the iteration multiple times, since the generation happens every time from scratch!

In Python 3, the range() was implemented like the xrange() function so that a dedicated xrange() function does not exist anymore (xrange() raises a NameError in Python 3).

Where Python 2 accepts both notations, the ‘old’ and the ‘new’ syntax, Python 3 chokes (and raises a SyntaxError in turn) if we don’t enclose the exception argument in parentheses.

answered Nov 26, 2015 by Gaurav