__future__

In [5]: from __future__ import
CO_FUTURE_ABSOLUTE_IMPORT   absolute_import
CO_FUTURE_DIVISION          all_feature_names
CO_FUTURE_PRINT_FUNCTION    division
CO_FUTURE_UNICODE_LITERALS  generators
CO_FUTURE_WITH_STATEMENT    nested_scopes
CO_GENERATOR_ALLOWED        print_function
CO_NESTED                   unicode_literals
_Feature                    with_statement

absolute_import

Forbidden implicit relative import, Not Forbidden explicit relative import

unicode_literals

# still running on Python 2.7

from __future__ import unicode_literals

print '\'xxx\' is unicode?', isinstance('xxx', unicode)
print 'u\'xxx\' is unicode?', isinstance(u'xxx', unicode)
print '\'xxx\' is str?', isinstance('xxx', str)
print 'b\'xxx\' is str?', isinstance(b'xxx', str)

Outputs

'xxx' is unicode? True
u'xxx' is unicode? True
'xxx' is str? False
b'xxx' is str? True

Problems

  • Python 2.x & Without unicode_literals

    Python 2.7.8 (default, Dec 11 2015, 13:09:06)
    Type "copyright", "credits" or "license" for more information.
    
    IPython 4.0.1 -- An enhanced Interactive Python.
    ?         -> Introduction and overview of IPython's features.
    %quickref -> Quick reference.
    help      -> Python's own help system.
    object?   -> Details about 'object', use 'object??' for extra details.
    
    In [1]: from datetime import datetime
    
    In [2]:
    
    In [2]: now = datetime.now()
    
    In [3]: print now.strftime('%m月%d日 %H:%M')
    05月17日 11:22
    
  • Python 2.x & With unicode_literals

    In [4]: from __future__ import unicode_literals
    
    In [5]: from datetime import datetime
    
    In [6]:
    
    In [6]: now = datetime.now()
    
    In [7]: print now.strftime('%m月%d日 %H:%M')
    ---------------------------------------------------------------------------
    UnicodeEncodeError                        Traceback (most recent call last)
    <ipython-input-7-765bdd22665e> in <module>()
    ----> 1 print now.strftime('%m月%d日 %H:%M')
    
    UnicodeEncodeError: 'ascii' codec can't encode character u'\u6708' in position 2: ordinal not in range(128)
    
  • Python 3.x

    Python 3.4.1 (default, Dec 11 2015, 12:11:12)
    Type "copyright", "credits" or "license" for more information.
    
    IPython 4.0.1 -- An enhanced Interactive Python.
    ?         -> Introduction and overview of IPython's features.
    %quickref -> Quick reference.
    help      -> Python's own help system.
    object?   -> Details about 'object', use 'object??' for extra details.
    
    In [1]: from datetime import datetime
    
    In [2]:
    
    In [2]: now = datetime.now()
    
    In [3]: print(now.strftime('%m月%d日 %H:%M'))
    05月17日 11:22
    

Reasons

  • Strftime accept string param in Python 2.x, when pass unicode, strftime will convert it.

Solutions

  • Solution No.1 — Runtime Encoding

    In [8]: from __future__ import unicode_literals
    
    In [9]: import sys
    
    In [10]: from datetime import datetime
    
    In [11]:
    
    In [11]: reload(sys)
    <module 'sys' (built-in)>
    
    In [12]: sys.setdefaultencoding('utf-8')
    
    In [13]:
    
    In [13]: now = datetime.now()
    
    In [14]: print now.strftime('%m月%d日 %H:%M')
    051711:22
    
  • Solution No.2 — Use Byte String

    In [15]: from __future__ import unicode_literals
    
    In [16]: from datetime import datetime
    
    In [17]:
    
    In [17]: now = datetime.now()
    
    In [18]: print now.strftime(b'%m月%d日 %H:%M')  # Appointed Bytearray String
    051711:22
    
    In [19]:
    
    In [19]: # Method Below Also Is OK
    
    In [20]: t = bytearray('%m月 %d %H:%M', 'utf-8')
    
    In [21]: print now.strftime(str(t))
    0517 11:22
    

References

[1] [email protected], 28.11. future — Future statement definitions

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