Changes between Version 63 and Version 64 of DeveloperGuidelines/CodeConventions

Timestamp:

01/20/18 21:17:16 (7 years ago)

Author:

Dominic König

Comment:

--

DeveloperGuidelines/CodeConventions

@@ -24 +24 @@
 {{{
 python static/scripts/tools/pep8.py yourfile.py
+}}}
+
+=== Print Statements ===
+
+For compatibility with WSGI as well as newer web2py (>=2.15), using the {{{print}}} statement in web application sources is strongly discouraged.
+
+CLI scripts containing print statements will even crash since gluon/shell.py now future-imports the Python-3 print_function.
+
+For everything that is to be executed in the restricted environment (i.e. all server code):
+ - use sys.stderr.write()
+ - better yet (and mandatory for any permanent debug/error messages): use {{{current.log.*}}}, as it can be turned on/off centrally, and routed to a log file
+ - if absolutely necessary, add the future-import to the file and use the print-function
+
+For CLI scripts:
+ - use sys.stderr.write() for status/error messages, or sys.stdout.write() for results
+ - alternatively, add the future-import to the script and use the print-function
+
+Using {{{sys.std*.write()}}} (remember that write expects string/bugger, so must convert explicitly):
+{{{#!python
+import sys
+
+# For status/error/debug messages:
+sys.stderr.write("Here is a status message\n")
+
+# For results:
+sys.stdout.write("%s\n" % result)
+}}}
+
+Using the logger:
+{{{#!python
+from gluon import current
+
+# Use this for any permanent message output in server scripts:
+current.log.error("Here is an error message")
+}}}
+
+If neither of the above is possible, import+use the print-function:
+{{{
+# This must be the first statement in the file:
+from __future__ import print_function
+
+# Then use the print-function:
+print("The print-function", "accepts", "multiple arguments")
+
+# Remember that server code must write to stderr, not stdout:
+print("Direct output to stderr", file=sys.stderr)
 }}}