Changes between Initial Version and Version 1 of DeveloperGuidelines/Py_2_3

Timestamp:

03/16/19 00:54:47 (6 years ago)

Author:

Dominic König

Comment:

--

DeveloperGuidelines/Py_2_3

@@ +1 @@
+= Python 2/3 Compatibility =
+[[TOC]]
+
+This guideline documents coding conventions to achieve hybrid Python-2.7/Python-3.5 compatibility in Sahana.
+
+It's a working document that will be added to as we move towards full Python-3 compatibility.
+
+== Syntax ==
+
+=== No print statements ===
+
+Don't use the print statement anywhere:
+{{{#!python
+print "example" # deprecated
+}}}
+
+You shouldn't use the print-function either, because it can clash with uWSGI:
+{{{#!python
+print("example") # not good
+}}}
+...but it can be tolerated in CLI scripts which don't run in the WSGI environment.
+
+Best option for debug output is to use sys.stderr.write:
+{{{#!python
+import sys
+sys.stderr.write("example\n") # better
+}}}
+
+...or the logger (as it can be configured globally to write to a log file instead of the system console):
+{{{#!python
+current.log.debug("example") # even better
+}}}
+
+=== Use as-syntax for catching exceptions ===
+
+When catching exceptions in a variable, don't use the comma-syntax:
+{{{#!python
+try:
+    ...
+except Exception, e: # deprecated
+    ...
+}}}
+
+Instead, use the as-keyword:
+{{{#!python
+try:
+    ...
+except Exception as e: # new standard
+    ...
+}}}
+
+=== No implicit package-relative imports ===
+
+Python-3 does not search for modules relative to the current module in the same package - unless explicitly indicated by leading {{{.}}} or {{{..}}} in the module path.
+
+{{{#!python
+from s3datetime import s3_format_datetime # inside modules/s3, not working in Python-3
+}}}
+
+Python-2.7 would search relative to the current module, but on the other hand, its supports the explicit-relative syntax as well. 
+
+So we decide that only explicit paths shall be used in imports.
+
+To import a module in the same package (e.g. within s3), either use explicit-relative syntax:
+{{{#!python
+from .s3datetime import s3_format_datetime # inside modules/s3, preferred variant
+}}}
+
+...or an absolute path relative to modules (or the global python path):
+{{{#!python
+from s3.s3datetime import s3_format_datetime # inside modules/s3, acceptable alternative
+}}}
+
+Outside of modules/s3, you should always import from the top-level of the s3 package (because the package structure may change over time):
+{{{#!python
+from s3 import s3_format_datetime # outside modules/s3
+}}}