Important differences between Python 2.x and Python 3.x with examples
If we are porting our code or executing python 3.x code in python 2.x, it can be dangerous if integer division changes go unnoticed (since it doesn’t raise any error). It is preferred to use the floating value (like 7.0/5 or 7/5.0) to get the expected result when porting our code.
This is the most well-known change. In this, the print keyword in Python 2.x is replaced by the print() function in Python 3.x. However, parentheses work in Python 2 if space is added after the print keyword because the interpreter evaluates it as an expression.
As we can see, if we use parentheses in python 2.x then there is no issue but if we don’t use parentheses in python 3.x, we get SyntaxError.
In Python 2, an implicit str type is ASCII. But in Python 3.x implicit str type is Unicode.
Python 2.x also supports Unicode
xrange() of Python 2.x doesn’t exist in Python 3.x. In Python 2.x, range returns a list i.e. range(3) returns [0, 1, 2] while xrange returns a xrange object i. e., xrange(3) returns iterator object which works similar to Java iterator and generates number when needed.
If we need to iterate over the same sequence multiple times, we prefer range() as range provides a static list. xrange() reconstructs the sequence every time. xrange() doesn’t support slices and other list methods. The advantage of xrange() is, it saves memory when the task is to iterate over a large range.
In Python 3.x, the range function now does what xrange does in Python 2.x, so to keep our code portable, we might want to stick to using a range instead. So Python 3.x’s range function is xrange from Python 2.x.
There is a small change in error handling in both versions. In python 3.x, ‘as’ keyword is required.
This is basically not a difference between the two versions, but a useful thing to mention here. The idea of the __future__ module is to help migrate to Python 3.x.
If we are planning to have Python 3.x support in our 2.x code, we can use _future_ imports in our code.
For example, in the Python 2.x code below, we use Python 3.x’s integer division behavior using the __future__ module.
Another example where we use brackets in Python 2.x using __future__ module:
Refer to this for more details of the __future__ module.
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