Stop using pkg_resources

tablib imports pkg_resources in order to find its own version. Importing
pkg_resources is very slow (100ms-250ms is common).

Avoid it by letting setuptools-scm generate a file with the version
instead.

.gitignore

@@ -38,3 +38,6 @@ htmlcov
 # setuptools noise
 .eggs
 *.egg-info
+
+# generated by setuptools-scm
+/src/tablib/_version.py

docs/conf.py

@@ -9,7 +9,7 @@
 #
 # All configuration values have a default; values that are commented out
 # serve to show the default.
-from pkg_resources import get_distribution
+import tablib
 
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
@@ -49,9 +49,9 @@ copyright = '2019 Jazzband'
 # built documents.
 #
 # The full version, including alpha/beta/rc tags.
-release = get_distribution('tablib').version
+release = tablib.__version__
 # The short X.Y version.
-version = '.'.join(release.split('.')[:2])
+version = '.'.join(tablib.__version__.split('.')[:2])
 # for example take major/minor
 
 # The language for content autogenerated by Sphinx. Refer to documentation

pyproject.toml

@@ -1,7 +1,7 @@
 [tool.isort]
 force_grid_wrap = 0
 include_trailing_comma = true
-known_third_party = ["MarkupPy", "odf", "openpyxl", "pkg_resources", "setuptools", "tablib", "xlrd", "xlwt", "yaml"]
+known_third_party = ["MarkupPy", "odf", "openpyxl", "setuptools", "tablib", "xlrd", "xlwt", "yaml"]
 line_length = 88
 multi_line_output = 3
 use_parentheses = true

setup.py

@@ -4,7 +4,9 @@ from setuptools import find_packages, setup
 
 setup(
     name='tablib',
-    use_scm_version=True,
+    use_scm_version={
+        'write_to': 'src/tablib/_version.py',
+    },
     setup_requires=['setuptools_scm'],
     description='Format agnostic tabular data library (XLS, JSON, YAML, CSV)',
     long_description=(

src/tablib/__init__.py

@@ -1,5 +1,12 @@
 """ Tablib. """
-from pkg_resources import DistributionNotFound, get_distribution
+try:
+    # Generated by setuptools-scm.
+    from ._version import version as __version__
+except ImportError:
+    # Some broken installation.
+    __version__ = None
+
+
 from tablib.core import (  # noqa: F401
     Databook,
     Dataset,
@@ -10,9 +17,3 @@ from tablib.core import (  # noqa: F401
     import_book,
     import_set,
 )
-
-try:
-    __version__ = get_distribution(__name__).version
-except DistributionNotFound:
-    # package is not installed
-    __version__ = None