inject_misc_tags no longer fails if document has no head. Resolves #16.

src/caterpillar.py

 #!/usr/bin/env python2
 # -*- coding: utf-8 -*-
 
 # Copyright 2015 Google Inc. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at
 #
 #     http://www.apache.org/licenses/LICENSE-2.0
@@ skipping 268 matching lines @@
   """
   Injects meta and link tags into an HTML document.
 
   Args:
     soup: BeautifulSoup HTML document. Will be modified.
     ca_manifest: Manifest dictionary of _Chrome App_.
     root_path: Path to the root directory of the web app from this HTML file.
       This can be either absolute or relative.
     html_path: Path to the HTML document being modified.
   """
+  if not soup.head:

[Matt Giuca, 2016/01/29 02:19:26]

head = soup.head
if not head:
  ...

Now you are guaranteed to have a "head" variable and you can replace instances
of "soup.head" below with just "head".

[Matthew Alger, 2016/01/29 02:41:51]

Okay, done. I'm not sure I see the benefit in this.

[Matt Giuca, 2016/01/29 03:04:13]

Mostly performance.

You generally want to avoid doing the same operation multiple times (and instead
storing it in a variable). Whether that's computations or just lookups, the same
principle applies (but it's less of a problem for lookups).

In Python (unlike static languages), member lookups are hash table lookups so
they are not free. And I don't know for sure, but I'd guess that this particular
lookup (in BeautifulSoup) may actually be an HTML tree search rather than a
simple hash lookup.

(Note: You should generally avoid micro-optimizations unless you have a pressing
performance need. But this sort of thing is more of a matter of good style/habit
than us specifically needing performance in this part of the program.)

+    head = soup.new_tag('head')
+    if soup.html:
+      soup.html.insert(0, head)
+    else:
+      soup.insert(0, head)
+
   # Add manifest link tag.
   manifest_path = os.path.join(root_path, PWA_MANIFEST_FILENAME)
   manifest_link = soup.new_tag('link', rel='manifest', href=manifest_path)
   soup.head.append(manifest_link)
 
   # Add meta tags (if they don't already exist).
   for tag in ('description', 'author', 'name'):
     if tag in ca_manifest and not soup('meta', {'name': tag}):
       meta = soup.new_tag('meta', content=ca_manifest[tag])
       meta['name'] = tag
@@ skipping 449 matching lines @@
   if args.mode == 'config':
     configuration.generate_and_save(args.output, args.interactive)
 
   elif args.mode == 'convert':
     config = configuration.load(args.config)
     convert_app(args.input, args.output, config, args.force)
 
 
 if __name__ == '__main__':
   sys.exit(main())