setup.py: add optional dependencies to extras_require

setup.py

@@ -30,6 +30,56 @@ wheel = ['wheel'] if needs_wheel else []
 needs_bumpversion = {'release'}.intersection(sys.argv)
 bumpversion = ['bump2version'] if needs_bumpversion else []
 
+extras_require = {
+	# for fontTools.ufoLib: to read/write UFO fonts
+	"ufo": [
+		"fs >= 2.1.1, < 3",
+		"enum34 >= 1.1.6; python_version < '3.4'",
+	],
+	# for fontTools.misc.etree and fontTools.misc.plistlib: use lxml to
+	# read/write XML files (faster/safer than built-in ElementTree)
+	"lxml": [
+		"lxml >= 4.0, < 5",
+		"singledispatch >= 3.4.0.3; python_version < '3.4'",
+	],
+	# for fontTools.sfnt and fontTools.woff2: to compress/uncompress
+	# WOFF 1.0 and WOFF 2.0 webfonts.
+	"woff": [
+		"brotli >= 1.0.1; platform_python_implementation != 'PyPy'",
+		"brotlipy >= 0.7.0; platform_python_implementation == 'PyPy'",
+		"zopfli >= 0.1.4",
+	],
+	# for fontTools.unicode and fontTools.unicodedata: to use the latest version
+	# of the Unicode Character Database instead of the built-in unicodedata
+	# which varies between python versions and may be outdated.
+	"unicode": [
+		# the unicodedata2 extension module doesn't work on PyPy.
+		# Python 3.7 already has Unicode 11, so the backport is not needed.
+		(
+			"unicodedata2 >= 11.0.0; "
+			"python_version < '3.7' and platform_python_implementation != 'PyPy'"
+		),
+	],
+	# for fontTools.interpolatable: to solve the "minimum weight perfect
+	# matching problem in bipartite graphs" (aka Assignment problem)
+	"interpolatable": [
+		# use pure-python alternative on pypy
+		"scipy; platform_python_implementation != 'PyPy'",
+		"munkres; platform_python_implementation == 'PyPy'",
+	],
+	# for fontTools.misc.symfont, module for symbolic font statistics analysis
+	"symfont": [
+		"sympy",
+	],
+	# To get file creator and type of Macintosh PostScript Type 1 fonts (macOS only)
+	"type1": [
+		"xattr; sys_platform == 'darwin'",
+	],
+}
+# use a special 'all' key as shorthand to includes all the extra dependencies
+extras_require["all"] = sum(extras_require.values(), [])
+
+
 # Trove classifiers for PyPI
 classifiers = {"classifiers": [
 	"Development Status :: 5 - Production/Stable",
@@ -307,6 +357,7 @@ setup(
 	tests_require=[
 		'pytest>=3.0',
 	],
+	extras_require=extras_require,
 	entry_points={
 		'console_scripts': [
 			"fonttools = fontTools.__main__:main",