update_payload: Fix most of lint styling issues.

This patch fixes a lot of pylint issues in the update_engine scripts. Majority
of this changes are based on recommendation found in:
	https://www.chromium.org/chromium-os/python-style-guidelines

It is a good idea to do these changes now, because if there are many pylint
errors when performing 'repo upload', serious problems can be overshadowed by a
lot of noise and eventually cause problems.

These fixes include:
	- Fixing executable shebangs to /usr/bin/python2.
	- Fixing import-error problems by disabiling them.
	- Removing pylint disables that are not valid anymore.
	- Changing all imports to proper absolute import format.
	- Change the import of PayloadError from update_payload.PayloadError for
	  simplicity.
	- Add pydoc strings for functions and classes that were missing.

The remaining unchanged pylint problmes include:

	- The header files of these scripts are in CrOS copyright format, but the
      the cros lint hook is configured to AoSP copyright format.
	- The test* functions in unittests are not compatible with CamelCase format.

BUG=chromium:796338
TEST=unittests pass
TEST=start_devserver
TEST=cros flash
TEST=scripts/paycheck.py

Change-Id: I7eed4d1625eb7c510c7949fada120de5a6a26c7b
Reviewed-on: https://chromium-review.googlesource.com/834875
Commit-Ready: Amin Hassani <ahassani@chromium.org>
Tested-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
Reviewed-by: Sen Jiang <senj@chromium.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/scripts/update_payload/applier.py b/scripts/update_payload/applier.py
index 3cb9741a..e470ac4e 100644
--- a/scripts/update_payload/applier.py
+++ b/scripts/update_payload/applier.py
@@ -24,8 +24,8 @@ import subprocess
 import sys
 import tempfile
 
-import common
-from error import PayloadError
+from update_payload import common
+from update_payload.error import PayloadError
 
 
 #
@@ -44,7 +44,6 @@ def _VerifySha256(file_obj, expected_hash, name, length=-1):
     PayloadError if computed hash doesn't match expected one, or if fails to
     read the specified length of data.
   """
-  # pylint: disable=E1101
   hasher = hashlib.sha256()
   block_length = 1024 * 1024
   max_length = length if length >= 0 else sys.maxint
@@ -316,6 +315,7 @@ class PayloadApplier(object):
     base_name = '%s.dst_extents' % op_name
 
     # Iterate over the extents and write zero.
+    # pylint: disable=unused-variable
     for ex, ex_name in common.ExtentIter(op.dst_extents, base_name):
       # Only do actual writing if this is not a pseudo-extent.
       if ex.start_block != common.PSEUDO_EXTENT_MARKER:
@@ -361,6 +361,7 @@ class PayloadApplier(object):
     """
 
     length = 0
+    # pylint: disable=unused-variable
     for ex, ex_name in common.ExtentIter(extents, base_name):
       length += ex.num_blocks * self.block_size
     return length