Remove unnecessary calls to dict.keys()

iter(dict) is equivalent to iter(dict.keys()), so simply act on the dict
instead of adding the extra call.

Inspired by Lennart Regebro's PyCon 2017 presentation "Prehistoric
Patterns in Python". Available at:

https://www.youtube.com/watch?v=V5-JH23Vk0I

PIL/IcoImagePlugin.py

@@ -176,8 +176,8 @@ class IcoFile(object):
             # figure out where AND mask image starts
             mode = a[0]
             bpp = 8
-            for k in BmpImagePlugin.BIT2MODE.keys():
-                if mode == BmpImagePlugin.BIT2MODE[k][1]:
+            for k, v in BmpImagePlugin.BIT2MODE.items():
+                if mode == v[1]:
                     bpp = k
                     break
 

PIL/Image.py

@@ -274,7 +274,7 @@ def _conv_type_shape(im):
         return shape+(extra,), typ
 
 
-MODES = sorted(_MODEINFO.keys())
+MODES = sorted(_MODEINFO)
 
 # raw modes that may be memory mapped.  NOTE: if you change this, you
 # may have to modify the stride calculation in map.c too!

PIL/IptcImagePlugin.py

@@ -95,7 +95,7 @@ class IptcImageFile(ImageFile.ImageFile):
                 tagdata = self.fp.read(size)
             else:
                 tagdata = None
-            if tag in list(self.info.keys()):
+            if tag in self.info:
                 if isinstance(self.info[tag], list):
                     self.info[tag].append(tagdata)
                 else:

Tests/test_file_jpeg.py

@@ -439,7 +439,7 @@ class TestFileJpeg(PillowTestCase):
     def test_no_duplicate_0x1001_tag(self):
         # Arrange
         from PIL import ExifTags
-        tag_ids = dict(zip(ExifTags.TAGS.values(), ExifTags.TAGS.keys()))
+        tag_ids = {v: k for k, v in ExifTags.TAGS.items()}
 
         # Assert
         self.assertEqual(tag_ids['RelatedImageWidth'], 0x1001)

Tests/test_file_libtiff.py

@@ -190,7 +190,7 @@ class TestFileLibTiff(LibTiffTestCase):
         # Exclude ones that have special meaning
         # that we're already testing them
         im = Image.open('Tests/images/hopper_g4.tif')
-        for tag in im.tag_v2.keys():
+        for tag in im.tag_v2:
             try:
                 del(core_items[tag])
             except:

Tests/test_imagecolor.py

@@ -119,7 +119,7 @@ class TestImageColor(PillowTestCase):
     # look for rounding errors (based on code by Tim Hatch)
     def test_rounding_errors(self):
 
-        for color in list(ImageColor.colormap.keys()):
+        for color in ImageColor.colormap:
             expected = Image.new(
                 "RGB", (1, 1), color).convert("L").getpixel((0, 0))
             actual = ImageColor.getcolor(color, 'L')

winbuild/build.py

@@ -12,7 +12,7 @@ from config import (compilers, compiler_from_env, pythons, pyversion_from_env,
 
 def setup_vms():
     ret = []
-    for py in pythons.keys():
+    for py in pythons:
         for arch in ('', X64_EXT):
             ret.append("virtualenv -p c:/Python%s%s/python.exe --clear %s%s%s"
                        % (py, arch, VIRT_BASE, py, arch))

winbuild/config.py

@@ -116,7 +116,7 @@ def pyversion_from_env():
     py = os.environ['PYTHON']
 
     py_version = '27'
-    for k in pythons.keys():
+    for k in pythons:
         if k in py:
             py_version = k
             break