pylint 1.7.5 caught some extra cases and failed Travis. [skip appveyor]

Makefile

@@ -151,20 +151,18 @@ $(PYPY):
 $(PYPY3):
 	scripts/install.sh pypy3
 
-PIP?=$(BUILD_RUNTIMES)/versions/$(PYTHON)/bin/pip
 
 develop:
 	ls -l $(BUILD_RUNTIMES)/snakepit/
-	echo pip is at `which $(PIP)`
 	echo python is at `which $(PYTHON)`
 # First install a newer pip so that it can use the wheel cache
 # (only needed until travis upgrades pip to 7.x; note that the 3.5
 # environment uses pip 7.1 by default)
-	${PIP} install -U pip setuptools
+	python -m pip install -U pip setuptools
 # Then start installing our deps so they can be cached. Note that use of --build-options / --global-options / --install-options
 # disables the cache.
 # We need wheel>=0.26 on Python 3.5. See previous revisions.
-	${PIP} install -U -r dev-requirements.txt
+	python -m pip install -U -r dev-requirements.txt
 
 lint-py27: $(PY27)
 	PYTHON=python2.7.14 PATH=$(BUILD_RUNTIMES)/versions/python2.7.14/bin:$(PATH) make develop travis_test_linters
@@ -177,22 +175,23 @@ test-py278: $(PY278)
 	PYTHON=python2.7.8 PATH=$(BUILD_RUNTIMES)/versions/python2.7.8/bin:$(PATH) make develop toxtest
 
 test-py34: $(PY34)
-	PYTHON=python3.4.7 PIP=pip PATH=$(BUILD_RUNTIMES)/versions/python3.4.7/bin:$(PATH) make develop toxtest
+	PYTHON=python3.4.7 PATH=$(BUILD_RUNTIMES)/versions/python3.4.7/bin:$(PATH) make develop toxtest
 
 test-py35: $(PY35)
-	PYTHON=python3.5.4 PIP=pip PATH=$(BUILD_RUNTIMES)/versions/python3.5.4/bin:$(PATH) make develop fulltoxtest
+	PYTHON=python3.5.4 PATH=$(BUILD_RUNTIMES)/versions/python3.5.4/bin:$(PATH) make develop fulltoxtest
 
 test-py36: $(PY36)
-	PYTHON=python3.6.2 PIP=pip PATH=$(BUILD_RUNTIMES)/versions/python3.6.2/bin:$(PATH) make develop toxtest
+	PYTHON=python3.6.2 PATH=$(BUILD_RUNTIMES)/versions/python3.6.2/bin:$(PATH) make develop toxtest
 
 test-py36-libuv: $(PY36)
 	GEVENT_CORE_CFFI_ONLY=libuv make test-py36
 
 test-pypy: $(PYPY)
-	PYTHON=$(PYPY) PIP=pip PATH=$(BUILD_RUNTIMES)/versions/pypy590/bin:$(PATH) make develop toxtest
+	ls $(BUILD_RUNTIMES)/versions/pypy590/bin/
+	PYTHON=$(PYPY) PATH=$(BUILD_RUNTIMES)/versions/pypy590/bin:$(PATH) make develop toxtest
 
 test-pypy3: $(PYPY3)
-	PYTHON=$(PYPY3) PIP=pip PATH=$(BUILD_RUNTIMES)/versions/pypy3.5_590/bin:$(PATH) make develop toxtest
+	PYTHON=$(PYPY3) PATH=$(BUILD_RUNTIMES)/versions/pypy3.5_590/bin:$(PATH) make develop toxtest
 
 test-py27-cffi: $(PY27)
 	GEVENT_CORE_CFFI_ONLY=1 PYTHON=python2.7.14 PATH=$(BUILD_RUNTIMES)/versions/python2.7.14/bin:$(PATH) make develop toxtest

src/gevent/_compat.py

@@ -22,7 +22,7 @@ if PY3:
 
 else:
     import __builtin__ # pylint:disable=import-error
-    string_types = __builtin__.basestring,
+    string_types = (__builtin__.basestring,)
     text_type = __builtin__.unicode
     integer_types = (int, __builtin__.long)
 

src/gevent/_ffi/loop.py

@@ -177,7 +177,7 @@ if sys.version_info[0] >= 3:
     integer_types = (int,)
 else:
     import __builtin__ # pylint:disable=import-error
-    basestring = __builtin__.basestring,
+    basestring = (__builtin__.basestring,)
     integer_types = (int, __builtin__.long)
 
 

src/gevent/libev/corecffi.py

@@ -124,7 +124,7 @@ if sys.version_info[0] >= 3:
     integer_types = (int,)
 else:
     import __builtin__ # pylint:disable=import-error
-    basestring = __builtin__.basestring,
+    basestring = (__builtin__.basestring,)
     integer_types = (int, __builtin__.long)