PEP 722: Fix reference implementation (gh-3284)

Author: pfmoore

pep-0722.rst

@@ -199,7 +199,7 @@ Recommendations
 ===============
 
 This section is non-normative and simply describes "good practices" when using
-metadata blocks.
+dependency blocks.
 
 While it is permitted for tools to do minimal validation of requirements, in
 practice they should do as much "sanity check" validation as possible, even if
@@ -234,23 +234,27 @@ reference implementation can be included here.
    def read_dependency_block(filename):
        # Use the tokenize module to handle any encoding declaration.
        with tokenize.open(filename) as f:
+           # Skip lines until we reach a dependency block (OR EOF).
            for line in f:
                if re.match(DEPENDENCY_BLOCK_MARKER, line):
-                   for line in f:
-                       if not line.startswith("#"):
-                           break
-                       # Remove comments. An inline comment is introduced by
-                       # a hash, which must be preceded and followed by a
-                       # space. The initial hash will be skipped as it has
-                       # no space before it.
-                       line = line.split(" # ", maxsplit=1)[0]
-                       line = line[1:].strip()
-                       if not line:
-                           break
-                       # Try to convert to a requirement. This will raise
-                       # an error if the line is not a PEP 508 requirement
-                       yield Requirement(line)
                    break
+           # Read dependency lines until we hit a line that doesn't
+           # start with #, or we are at EOF.
+           for line in f:
+               if not line.startswith("#"):
+                   break
+               # Remove comments. An inline comment is introduced by
+               # a hash, which must be preceded and followed by a
+               # space.
+               line = line[1:].split(" # ", maxsplit=1)[0]
+               line = line.strip()
+               # Ignore empty lines
+               if not line:
+                   continue
+               # Try to convert to a requirement. This will raise
+               # an error if the line is not a PEP 508 requirement
+               yield Requirement(line)
+
 
 A format similar to the one proposed here is already supported `in pipx
 <https://github.com/pypa/pipx/pull/916>`__ and in `pip-run
@@ -366,7 +370,7 @@ no real benefit.
 
 So the question is essentially, "why not use TOML?"
 
-The key idea behind the "metadata block" format is to define something that
+The key idea behind the "dependency block" format is to define something that
 reads naturally as a comment in the script. Dependency data is useful both for
 tools and for the human reader, so having a human readable format is beneficial.
 On the other hand, TOML of necessity has a syntax of its own, which distracts