What is future in Python used for and how when to use it and how it works

Question

future   frequently appears in Python modules  I do not understand what   future   is for and how when to use it even after reading the Python s   future   doc    Can anyone explain with examples   A few answers regarding the basic usage of   future   I ve received seemed correct    However  I need to understand one more thing regarding how   future   works   The most confusing concept for me is how a current python release includes features for future releases  and how a program using a feature from a future release can be be compiled successfully in the current version of Python   I am guessing that the current release is packaged with potential features for the future  However  the features are available only by using   future   because they are not the current standard  Let me know if I am right

User · Answer

One of the uses which I found to be very useful is the print_function from __future__ module.

In Python 2.7, I wanted chars from different print statements to be printed on same line without spaces.

It can be done using a comma(",") at the end, but it also appends an extra space. The above statement when used as :

from __future__ import print_function
...
print (v_num,end="")
...

This will print the value of v_num from each iteration in a single line without spaces.

User · Answer

There are some great answers already  but none of them address a complete list of what the   future   statement currently supports   Put simply  the   future   statement forces Python interpreters to use newer features of the language      The features that it currently supports are the following   nested scopes  Prior to Python 2 1  the following code would raise a NameError   def f                def g value                       return g value-1    1           The from   future   import nested scopes directive will allow for this feature to be enabled   generators  Introduced generator functions such as the one below to save state between successive function calls   def fib        a  b   0  1     while 1         yield b        a  b   b  a b   division  Classic division is used in Python 2 x versions  Meaning that some division statements return a reasonable approximation of division   true division   and others return the floor   floor division    Starting in Python 3 0  true division is specified by x y  whereas floor division is specified by x  y    The from   future   import division directive forces the use of Python 3 0 style division   absolute import  Allows for parenthesis to enclose multiple import statements  For example   from Tkinter import  Tk  Frame  Button  Entry  Canvas  Text      LEFT  DISABLED  NORMAL  RIDGE  END    Instead of   from Tkinter import Tk  Frame  Button  Entry  Canvas  Text        LEFT  DISABLED  NORMAL  RIDGE  END   Or   from Tkinter import Tk  Frame  Button  Entry  Canvas  Text from Tkinter import LEFT  DISABLED  NORMAL  RIDGE  END   with statement  Adds the statement with as a keyword in Python to eliminate the need for try finally statements  Common uses of this are when doing file I O such as   with open  workfile    r   as f       read data   f read     print function   Forces the use of Python 3 parenthesis-style print   function call instead of the print MESSAGE style statement   unicode literals  Introduces the literal syntax for the bytes object  Meaning that statements such as bytes  Hello world    ascii   can be simply expressed as b Hello world    generator stop  Replaces the use of the StopIteration exception used inside generator functions with the RuntimeError exception   One other use not mentioned above is that the   future   statement also requires the use of Python 2 1  interpreters since using an older version will throw a runtime exception     References   https   docs python org 2 library future html https   docs python org 3 library future html https   docs python org 2 2 whatsnew node9 html https   www python org dev peps pep-0255  https   www python org dev peps pep-0238  https   www python org dev peps pep-0328  https   www python org dev peps pep-3112  https   www python org dev peps pep-0479

User · Answer

It can be used to use features which will appear in newer versions while having an older release of Python   For example   gt  gt  gt  from   future   import print function   will allow you to use print as a function    gt  gt  gt  print    of entries   len dictionary   file sys stderr

User · Answer

Or is it like saying  Since this is python v2 7  use that different  print  function that has also been added to python v2 7  after it was added in python 3  So my  print  will no longer be statements  eg print  message    but functions  eg  print  message   options   That way when my code is run in python 3   print  will not break    In   from   future   import print function   print function is the module containing the new implementation of  print  as per how it is behaving in python v3   This has more explanation  http   python3porting com noconv html

User · Answer

future   is a pseudo-module which programmers can use to enable new language features which are not compatible with the current interpreter  For example  the expression 11 4 currently evaluates to 2  If the module in which it is executed had enabled true division by executing   from   future   import division  the expression 11 4 would evaluate to 2 75  By importing the   future   module and evaluating its variables  you can see when a new feature was first added to the language and when it will become the default      gt  gt  gt  import   future      gt  gt  gt    future   division    Feature  2  2  0   alpha   2    3  0  0   alpha   0   8192

User · Answer

With   future   module s inclusion  you can slowly be accustomed to incompatible changes or to such ones introducing new keywords   E g   for using context managers  you had to do from   future   import with statement in 2 5  as the with keyword was new and shouldn t be used as variable names any longer  In order to use with as a Python keyword in Python 2 5 or older  you will need to use the import from above   Another example is  from   future   import division print 8 7    prints 1 1428571428571428 print 8  7   prints 1   Without the   future   stuff  both print statements would print 1   The internal difference is that without that import    is mapped to the   div     method  while with it    truediv     is used   In any case     calls   floordiv        Apropos print  print becomes a function in 3 x  losing its special property as a keyword  So it is the other way round    gt  gt  gt  print   gt  gt  gt  from   future   import print function  gt  gt  gt  print  lt built-in function print gt   gt  gt  gt

User · Answer

When you do  from   future   import whatever   You re not actually using an import statement  but a future statement  You re reading the wrong docs  as you re not actually importing that module   Future statements are special -- they change how your Python module is parsed  which is why they must be at the top of the file  They give new -- or different -- meaning to words or symbols in your file  From the docs      A future statement is a directive to the compiler that a particular module should be compiled using syntax or semantics that will be available in a specified future release of Python  The future statement is intended to ease migration to future versions of Python that introduce incompatible changes to the language  It allows use of the new features on a per-module basis before the release in which the feature becomes standard    If you actually want to import the   future   module  just do  import   future     and then access it as usual

User · Answer

After Python 3 0 onward  print is no longer just a statement  its a function instead  and is included in PEP 3105    Also I think the Python 3 0 package has still these special functionality  Lets see its usability through a traditional  Pyramid program  in Python   from   future   import print function  class Star object       def   init   self count           self count   count      def start self           for i in range 1 self count               for j in range  i                    print      end       PEP 3105  print As a Function              print    a   Star 5  a start    Output                  If we use normal print function  we won t be able to achieve the same output  since print   comes with a extra newline  So every time the inner for loop execute  it will print   onto the next line

[python] What is future in Python used for and how/when to use it, and how it works

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