Python 2 and 3 compatibility¶
The code must be compatible Python versions 2.7 and 3.6+.
Here are the basic rules to follow for all new code. Existing code needs to be revised to follow these rules. See the official guide for general rules.
Always use absolute imports. Import absolute imports from future to disable relative imports.
from __future__ import absolute_import
Use loggers instead of print when possible. When using print, use it as a function with parenthesis. Include print from future to disable Python 2 style print.
from __future__ import print_function
from __future__ import division
to make sure that division acts the Python 3 way. Use
// when you need integer division.
All text should be Unicode. Encode Unicode text from and to bytes using UTF-8 encoding when doing I/O operations. Encoding and decoding is done as close as possible to the I/O operations. Some people refer to that as the Unicode sandwich.
By default, string literals are byte strings in Python 2 and Unicode strings in Python 3. Import Unicode literals from future to make all string literals Unicode in any Python version.
from __future__ import unicode_literals
When you really need a byte string literal create it with
opensfm.io.open_wt to open text files for reading and writing. This functions take care of decoding and encoding UTF-8 files from and into Unicode.
opensfm.io.json_dumps to encode and decode JSON documents. This functions make sure that the JSON representation is Unicode text and that, when written in a file, it is written using UTF-8 encoding.