Remove Python 2 (pantsbuild#56)

Eric-Arellano · web-flow · commit 2a6f66ce8a45 · 2020-11-24T15:01:22.000-07:00
Demonstrating Python 2 is no longer pulling its weight. Python 2 interpreters are becoming harder to come by, and there are some issues with it like PyYAML failing to be built on macOS Big Sur when using a Python 2 interpreter.

Instead, we might want a dedicated example repo for Python 2 -&gt; 3 repos. It can be more focused, such as not showing off Protobuf.
diff --git a/.travis.yml b/.travis.yml
@@ -24,4 +24,3 @@ script:
   # We also smoke test that our release process will work by running `package`.
   - ./pants lint typecheck test package '::'
   - ./pants run helloworld/main.py
-  - ./pants run helloworld/main_py2.py
diff --git a/BUILD b/BUILD
@@ -6,19 +6,19 @@
 # with the name of the corresponding dist.
 #
 # For example, `translate>=3.2.1` expands to:
+#
 #   python_requirement_library(
 #     name='translate',
-#     requirements=[
-#       python_requirement('translate>=3.2.1')
-#     ]
+#     requirements=['translate>=3.2.1']
 #   )
 #
-# Refer to https://www.pantsbuild.org/v2.0/docs/python-third-party-dependencies.
-
+# We set `module_mapping` for any requirements whose module names differ from the project's name so that dependency
+# inference works.
+#
+# Refer to https://www.pantsbuild.org/docs/python-third-party-dependencies.
 python_requirements(
-  # `setuptools` exposes a module different than the project name. We teach this to Pants so that
-  # it can correctly infer dependencies.
   module_mapping={
+    "ansicolors": ["colors"],
     "setuptools": ["pkg_resources"],
   },
 )
diff --git a/README.md b/README.md
@@ -144,7 +144,7 @@ Try these out in this repo!
 ## Create a PEX binary
 
 ```
-./pants package helloworld/main.py helloworld/main_py2.py
+./pants package helloworld/main.py
 ```
 
 ## Run a binary
diff --git a/build-support/generate_constraints.sh b/build-support/generate_constraints.sh
@@ -16,10 +16,3 @@ CONSTRAINTS_FILE=constraints.txt
 "${PIP}" install -r <(./pants dependencies --type=3rdparty ::)
 echo "# Generated by build-support/generate_constraints.sh on $(date)" > "${CONSTRAINTS_FILE}"
 "${PIP}" freeze --all >> "${CONSTRAINTS_FILE}"
-
-# This example repo includes some Python 2-only code for demonstration. Because we generated
-# the constraints using Python 3.7, we must manually ensure things still work with Python 2.7. So,
-# we warn to the user that they should check the diff. You can delete this if you don't use Python 2.
-echo "Check the diff for ${CONSTRAINTS_FILE} and restore any entries that were specific to" \
-  "Python 2, i.e. entries ending in \`python_version == '2.7'\`. Those are needed for Python 2 to" \
-  "work properly, and this script will overwrite it." 1>&2
diff --git a/constraints.txt b/constraints.txt
@@ -1,36 +1,32 @@
-# Generated by build-support/generate_constraints.sh on Wed Sep 16 11:30:54 MST 2020
+# Generated by build-support/generate_constraints.sh on Tue Nov 24 13:57:41 MST 2020
 ansicolors==1.1.8
 appdirs==1.4.4
 certifi==2020.6.20
-cfgv==2.0.1 ; python_version == '2.7'
-cfgv==3.1.0 ; python_version > '2.7'
+cfgv==3.2.0
 chardet==3.0.4
 click==7.1.2
 distlib==0.3.1
 filelock==3.0.12
-identify==1.5.2
+identify==1.5.5
 idna==2.10
 importlib-metadata==1.7.0
 importlib-resources==3.0.0
 lxml==4.5.2
 nodeenv==1.5.0
 packaging==20.4
-pip==20.2.3
+pip==20.2.4
 pluggy==0.13.1
-pre-commit==1.21.0 ; python_version == '2.7'
-pre-commit==2.7.1 ; python_version > '2.7'
+pre-commit==2.7.1
 protobuf==3.13.0
 py==1.9.0
 pyparsing==2.4.7
 PyYAML==5.3.1
 requests==2.24.0
-setuptools==44.1.1 ; python_version == '2.7'
-setuptools==50.3.0 ; python_version > '2.7'
+setuptools==50.3.0
 six==1.15.0
 toml==0.10.1
 tox==3.20.0
 translate==3.5.0
 urllib3==1.25.10
-virtualenv==20.0.31
-zipp==1.2.0 ; python_version == '2.7'
-zipp==3.1.0 ; python_version > '2.7'
+virtualenv==20.0.33
+zipp==3.3.0
diff --git a/helloworld/BUILD b/helloworld/BUILD
@@ -1,19 +1,12 @@
 # Copyright 2020 Pants project contributors.
 # Licensed under the Apache License, Version 2.0 (see LICENSE).
 
+# `name` defaults to the name of this directory, i.e., `helloworld`.
 pex_binary(
-    # name defaults to the name of this directory, i.e., `helloworld`.
     sources=["main.py"],
     entry_point="helloworld.main",
 )
 
-pex_binary(
-    name="helloworld_py2",
-    sources=["main_py2.py"],
-    entry_point="helloworld.main_py2",
-    interpreter_constraints=["==2.7.*"],
-)
-
 python_library(
   name="awslambda_lib",
   sources=["awslambda.py"],
@@ -27,15 +20,11 @@ python_awslambda(
     runtime="python3.7",
 )
 
+# Pants cannot infer dependencies on resources targets and Protobuf, so we explicitly add them.
 python_library(
     name="config",
     sources=["config.py"],
-    dependencies=[
-        # Pants cannot infer dependencies on resources targets and Protobuf, so we explicitly
-        # add them.
-        ":config_file",
-        "helloworld/util/proto",
-    ],
+    dependencies=[":config_file", "helloworld/util/proto"],
 )
 
 resources(
diff --git a/helloworld/greet_py2/BUILD b/helloworld/greet_py2/BUILD
diff --git a/helloworld/greet_py2/__init__.py b/helloworld/greet_py2/__init__.py
diff --git a/helloworld/greet_py2/greeting_py2.py b/helloworld/greet_py2/greeting_py2.py
diff --git a/helloworld/main_py2.py b/helloworld/main_py2.py
diff --git a/helloworld/util/BUILD b/helloworld/util/BUILD
@@ -1,38 +1,34 @@
 # Copyright 2020 Pants project contributors.
 # Licensed under the Apache License, Version 2.0 (see LICENSE).
 
-# See https://www.pantsbuild.org/docs/python-setup-py-goal.
-python_distribution(
-  name="dist",
-  # Because this has no source code, Pants cannot infer dependencies.
-  dependencies=[":util"],
-  setup_py_commands=["bdist_wheel", "sdist"],
-  provides=setup_py(
-      name='helloworld.util',
-      version='0.0.1',
-      description='Greeting library utilities.',
-  ),
-)
-
 # `name` defaults to the name of this directory, i.e., `util`.
 # `sources` defaults to ['*.py', '!*_test.py', '!test_*.py', '!conftest.py'].
+# `dependencies` is set because only Pants 2.2+ can infer dependencies on Protobuf.
 python_library(
-  # Pants cannot infer dependencies on Protobuf, so we explicitly add it.
-  dependencies=[
-      "helloworld/util/proto",
-  ],
+    dependencies=["helloworld/util/proto"],
 )
 
+# `sources` defaults to ['*_test.py', 'test_*.py', 'conftest.py'].
+# Pants cannot infer dependencies on `resources` targets, so we explicitly add the dep.
 python_tests(
     name='tests',
-    # `sources` defaults to ['*_test.py', 'test_*.py', 'conftest.py'].
-    # Pants cannot infer dependencies on `resources` targets, so we explicitly add it.
-    dependencies=[
-        ":config_loader_test_data",
-    ],
+    dependencies=[":test_data"],
 )
 
 resources(
-    name='config_loader_test_data',
-    sources=['config_loader_test_data.json'],
+    name='test_data',
+    sources=['*_test_data.json'],
+)
+
+# See https://www.pantsbuild.org/docs/python-distributions.
+# Because this target has no source code, Pants cannot infer dependencies.
+python_distribution(
+    name="dist",
+    dependencies=[":util"],
+    setup_py_commands=["bdist_wheel", "sdist"],
+    provides=setup_py(
+        name='helloworld.util',
+        version='0.0.1',
+        description='Greeting library utilities.',
+    ),
 )
diff --git a/helloworld/util/proto/BUILD b/helloworld/util/proto/BUILD
@@ -3,14 +3,9 @@
 
 # `name` defaults to the name of this directory, i.e., `proto`.
 # `sources` defaults to ["*.proto"].
-protobuf_library(dependencies=[":init"])
+protobuf_library()
 
-
-# Note that we need an `__init__.py` file for MyPy to recognize our generated code as a valid
-# module. We include this in the dependencies for the `protobuf_library` to ensure the
-# `__init__.py` is always used.
-#
-# Often, you won't want to put `__init__.py` files in your Protobuf directories; see
-# https://www.pantsbuild.org/docs/protobuf#protobuf-and-source-roots for how to change where the
-# protobuf code is generated.
-python_library(name="init")
+# Note that we have an empty `__init__.py` file in this folder. Pants will generate
+# `helloworld/util/proto/config_pb2.py`, and we need an `__init__.py` file in the folder for that file to be properly
+# recognized. Pants will automatically use this `__init__.py` file if it exists, even though we don't have a
+# `python_library` target here.
diff --git a/pants.toml b/pants.toml
@@ -14,9 +14,6 @@ backend_packages.add = [
   "pants.backend.python.lint.flake8",
   "pants.backend.python.lint.isort",
   "pants.backend.python.typecheck.mypy",
-  # Adds the `py-constraints` goal, as this example repository has
-  # both Python 2 and Python 3 code.
-  "pants.backend.python.mixed_interpreter_constraints",
 ]
 
 [source]
