1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
|
.. _translation:
Using Python 2-only dependencies on Python 3
--------------------------------------------
The ``past`` module provides an experimental ``translation`` package to help
with importing and using old Python 2 modules in a Python 3 environment.
This is implemented using PEP 414 import hooks together with fixers from
``lib2to3`` and ``libfuturize`` (included with ``python-future``) that
attempt to automatically translate Python 2 code to Python 3 code with equivalent
semantics upon import.
*Note* This feature is still in alpha and needs further development to support a
full range of real-world Python 2 modules. Also be aware that the API for
this package might change considerably in later versions.
Here is how to use it::
$ pip3 install plotrique==0.2.5-7 --no-compile # to ignore SyntaxErrors
$ python3
Then pass in a whitelist of module name prefixes to the
``past.translation.autotranslate()`` function. Example::
>>> from past.translation import autotranslate
>>> autotranslate(['plotrique'])
>>> import plotrique
Here is another example::
>>> from past.translation import install_hooks, remove_hooks
>>> install_hooks(['mypy2module'])
>>> import mypy2module
>>> remove_hooks()
This will translate, import and run Python 2 code such as the following::
### File: mypy2module.py
# Print statements are translated transparently to functions:
print 'Hello from a print statement'
# xrange() is translated to Py3's range():
total = 0
for i in xrange(10):
total += i
print 'Total is: %d' % total
# Dictionary methods like .keys() and .items() are supported and
# return lists as on Python 2:
d = {'a': 1, 'b': 2}
assert d.keys() == ['a', 'b']
assert isinstance(d.items(), list)
# Functions like range, reduce, map, filter also return lists:
assert isinstance(range(10), list)
# The exec statement is supported:
exec 'total += 1'
print 'Total is now: %d' % total
# Long integers are supported:
k = 1234983424324L
print 'k + 1 = %d' % k
# Most renamed standard library modules are supported:
import ConfigParser
import HTMLParser
import urllib
The attributes of the module are then accessible normally from Python 3.
For example::
# This Python 3 code works
>>> type(mypy2module.d)
builtins.dict
This is a standard Python 3 data type, so, when called from Python 3 code,
``keys()`` returns a view, not a list::
>>> type(mypy2module.d.keys())
builtins.dict_keys
.. _translation-limitations:
Known limitations of ``past.translation``
*****************************************
- It currently requires a newline at the end of the module or it throws a
``ParseError``.
- This only works with pure-Python modules. C extension modules and Cython code
are not supported.
- The biggest hurdle to automatic translation is likely to be ambiguity
about byte-strings and text (unicode strings) in the Python 2 code. If the
``past.autotranslate`` feature fails because of this, you could try
running ``futurize`` over the code and adding a ``b''`` or ``u''`` prefix to
the relevant string literals. To convert between byte-strings and text (unicode
strings), add an ``.encode`` or ``.decode`` method call. If this succeeds,
please push your patches upstream to the package maintainers.
- Otherwise, the source translation feature offered by the ``past.translation``
package has similar limitations to the ``futurize`` script (see
:ref:`futurize-limitations`). Help developing and testing this feature further
would be particularly welcome.
Please report any bugs you find on the ``python-future`` `bug tracker
<https://github.com/PythonCharmers/python-future/>`_.
|
