[docs] Document afmLib (#1933)

Doc/source/afmLib.rst

@@ -1,8 +1,8 @@
-######
-afmLib
-######
+###########################################
+afmLib: Read/write Adobe Font Metrics files
+###########################################
 
 .. automodule:: fontTools.afmLib
-   :inherited-members:
+
+.. autoclass:: fontTools.afmLib.AFM
    :members:
-   :undoc-members:

Lib/fontTools/afmLib.py

@@ -1,8 +1,50 @@
-"""Module for reading and writing AFM files."""
+"""Module for reading and writing AFM (Adobe Font Metrics) files.
+
+Note that this has been designed to read in AFM files generated by Fontographer
+and has not been tested on many other files. In particular, it does not
+implement the whole Adobe AFM specification [#f1]_ but, it should read most
+"common" AFM files.
+
+Here is an example of using `afmLib` to read, modify and write an AFM file:
+
+	>>> from fontTools.afmLib import AFM
+	>>> f = AFM("Tests/afmLib/data/TestAFM.afm")
+	>>>
+	>>> # Accessing a pair gets you the kern value
+	>>> f[("V","A")]
+	-60
+	>>>
+	>>> # Accessing a glyph name gets you metrics
+	>>> f["A"]
+	(65, 668, (8, -25, 660, 666))
+	>>> # (charnum, width, bounding box)
+	>>>
+	>>> # Accessing an attribute gets you metadata
+	>>> f.FontName
+	'TestFont-Regular'
+	>>> f.FamilyName
+	'TestFont'
+	>>> f.Weight
+	'Regular'
+	>>> f.XHeight
+	500
+	>>> f.Ascender
+	750
+	>>>
+	>>> # Attributes and items can also be set
+	>>> f[("A","V")] = -150 # Tighten kerning
+	>>> f.FontName = "TestFont Squished"
+	>>>
+	>>> # And the font written out again
+	>>> f.write("testfont-squished.afm")
+
+.. rubric:: Footnotes
+
+.. [#f1] `Adobe Technote 5004 <https://www.adobe.com/content/dam/acom/en/devnet/font/pdfs/5004.AFM_Spec.pdf>`_,
+   Adobe Font Metrics File Format Specification.
+
+"""
 
-# XXX reads AFM's generated by Fog, not tested with much else.
-# It does not implement the full spec (Adobe Technote 5004, Adobe Font Metrics
-# File Format Specification). Still, it should read most "common" AFM files.
 
 from fontTools.misc.py23 import *
 import re
@@ -97,6 +139,11 @@ class AFM(object):
 			]
 
 	def __init__(self, path=None):
+		"""AFM file reader.
+
+		Instantiating an object with a path name will cause the file to be opened,
+		read, and parsed. Alternatively the path can be left unspecified, and a
+		file can be parsed later with the :meth:`read` method."""
 		self._attrs = {}
 		self._chars = {}
 		self._kerning = {}
@@ -107,6 +154,7 @@ def __init__(self, path=None):
 			self.read(path)
 
 	def read(self, path):
+		"""Opens, reads and parses a file."""
 		lines = readlines(path)
 		for line in lines:
 			if not line.strip():
@@ -189,6 +237,7 @@ def parsecomposite(self, rest):
 		self._composites[charname] = components
 
 	def write(self, path, sep='\r'):
+		"""Writes out an AFM font to the given path."""
 		import time
 		lines = [	"StartFontMetrics 2.0",
 				"Comment Generated by afmLib; at %s" % (
@@ -258,24 +307,40 @@ def myKey(a):
 		writelines(path, lines, sep)
 
 	def has_kernpair(self, pair):
+		"""Returns `True` if the given glyph pair (specified as a tuple) exists
+		in the kerning dictionary."""
 		return pair in self._kerning
 
 	def kernpairs(self):
+		"""Returns a list of all kern pairs in the kerning dictionary."""
 		return list(self._kerning.keys())
 
 	def has_char(self, char):
+		"""Returns `True` if the given glyph exists in the font."""
 		return char in self._chars
 
 	def chars(self):
+		"""Returns a list of all glyph names in the font."""
 		return list(self._chars.keys())
 
 	def comments(self):
+		"""Returns all comments from the file."""
 		return self._comments
 
 	def addComment(self, comment):
+		"""Adds a new comment to the file."""
 		self._comments.append(comment)
 
 	def addComposite(self, glyphName, components):
+		"""Specifies that the glyph `glyphName` is made up of the given components.
+		The components list should be of the following form::
+
+			[
+				(glyphname, xOffset, yOffset),
+				...
+			]
+		
+		"""
 		self._composites[glyphName] = components
 
 	def __getattr__(self, attr):