[Python] Use explicit imports

[practicalswift]

No description provided.

[modocache]

This change causes an error:

apple/swift $ ./utils/cmpcodesize/cmpcodesize.py -h
Traceback (most recent call last):
  File "./utils/cmpcodesize/cmpcodesize.py", line 6, in <module>
    cmpcodesize.main()
AttributeError: 'module' object has no attribute 'main'

[modocache]

The error could be fixed with a corresponding change to utils/cmpcodesize/cmpcodesize.py:

diff --git a/utils/cmpcodesize/cmpcodesize.py b/utils/cmpcodesize/cmpcodesize.py
index 0390af7..eb9ecfa 100755
--- a/utils/cmpcodesize/cmpcodesize.py
+++ b/utils/cmpcodesize/cmpcodesize.py
@@ -1,6 +1,6 @@
 #!/usr/bin/env python

-import cmpcodesize
+from cmpcodesize.main import main

 if __name__ == '__main__':
-    cmpcodesize.main()
+    main()

Which I wouldn't be opposed to. I wrote it this way because it mirrored the structure of llvm/utils/lit/lit.py.

[modocache]

I'm curious, though: is it bad form to use this style of relative imports? If so, should a corresponding change be proposed to llvm/utils/lit as well?

/cc @ddunbar, author of lit

[modocache]

nit: How about instead:

from SwiftBuildSupport import (
    SWIFT_SOURCE_ROOT,
    SWIFT_BUILD_ROOT,
    print_with_argv0,
    quote_shell_command,
    check_call,
    get_preset_options,
    get_all_preset_names
)

I've seen this import style suggested in a few style guides:

• https://www.python.org/dev/peps/pep-0328/
• http://docs.python-guide.org/en/latest/writing/style/

[practicalswift]

@modocache Thanks a lot for reviewing! I've updated accordingly. Please take a look at the updated code :-)

[gribozavr]

@practicalswift I think this is an improvement, but I would recommend to switch to the code formatting suggested by @modocache:

from SwiftBuildSupport import (
    SWIFT_SOURCE_ROOT,
    SWIFT_BUILD_ROOT,
    print_with_argv0,
    quote_shell_command,
    check_call,
    get_preset_options,
    get_all_preset_names
)

since we normally don't do "endline" layout in Python code.

[practicalswift]

@gribozavr Fixed :-)

[modocache]

Looks great! Thanks for updating. I'll follow up with @ddunbar about how lit is structured.