Reduce complexity in pmbootstrap.py (#160)

Thanks, @cclauss!

* Dictionary lookup of event loop actions

This was kind of an experiment that adds lots of blank lines to this script -- feel free to reject it.

The observation that triggered this was that in main() all actions can execute using just one parameter, args.  This means that it is possible to use args.action to do a dict lookup to get the corresponding function.  This approach adds tons of blank lines to the script in exchange for a rapid seek to the action implementation and a substantial reduction of the McCabe complexity of main().

$ __flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics__
```
./pmbootstrap.py:43:1: C901 'main' is too complex (23)
./pmb/aportgen/core.py:38:1: C901 'rewrite' is too complex (17)
[ ... ]
```

* Remove action_dict and use locals() instead

pmbootstrap.py

@@ -40,6 +40,84 @@ import pmb.parse
 import pmb.install
 
 
+def action_aportgen(args):
+    pmb.aportgen.generate(args, args.package)
+
+
+def action_build(args):
+    pmb.build.package(args, args.package, args.arch, args.force,
+                      args.buildinfo)
+
+
+def action_build_init(args):
+    pmb.build.init(args, args.suffix)
+
+
+def action_challenge(args):
+    pmb.challenge.frontend(args)
+
+
+def action_checksum(args):
+    pmb.build.checksum(args, args.package)
+
+
+def action_chroot(args):
+    pmb.chroot.apk.check_min_version(args, args.suffix)
+    pmb.chroot.root(args, args.command, args.suffix, log=False)
+
+
+def action_index(args):
+    pmb.build.index_repo(args)
+
+
+def action_initfs(args):
+    pmb.chroot.initfs.frontend(args)
+
+
+def action_install(args):
+    pmb.install.install(args)
+
+
+def action_flasher(args):
+    pmb.flasher.frontend(args)
+
+
+def action_menuconfig(args):
+    pmb.build.menuconfig(args, args.package, args.deviceinfo["arch"])
+
+
+def action_parse_apkbuild(args):
+    build_path = args.aports + "/" + args.package + "/APKBUILD"
+    print(json.dumps(pmb.parse.apkbuild(args, build_path), indent=4))
+
+
+def action_parse_apkindex(args):
+    result = pmb.parse.apkindex.parse(args, args.apkindex_path)
+    print(json.dumps(result, indent=4))
+
+
+def action_shutdown(args):
+    pmb.chroot.shutdown(args)
+
+
+def action_stats(args):
+    pmb.build.ccache_stats(args, args.arch)
+
+
+def action_log(args):
+    pmb.helpers.run.user(args, ["tail", "-f", args.log, "-n", args.lines],
+                         log=False)
+
+
+def action_log_distccd(args):
+    logpath = "/home/user/distccd.log"
+    pmb.chroot.user(args, ["tail", "-f", logpath, "-n", args.lines], log=False)
+
+
+def action_zap(args):
+    pmb.chroot.zap(args)
+
+
 def main():
     # Parse arguments, set up logging
     args = pmb.parse.arguments()
@@ -53,58 +131,15 @@ def main():
         # Initialize or require config
         if args.action == "init":
             return pmb.config.init(args)
-        if not os.path.exists(args.config):
+        elif not os.path.exists(args.config):
             logging.critical("Please specify a config file, or run"
                              " 'pmbootstrap init' to generate one.")
             return 1
 
-        # All other actions
-        if args.action == "aportgen":
-            pmb.aportgen.generate(args, args.package)
-        elif args.action == "build":
-            pmb.build.package(args, args.package, args.arch, args.force,
-                              args.buildinfo)
-        elif args.action == "build_init":
-            pmb.build.init(args, args.suffix)
-        elif args.action == "challenge":
-            pmb.challenge.frontend(args)
-        elif args.action == "checksum":
-            pmb.build.checksum(args, args.package)
-        elif args.action == "chroot":
-            pmb.chroot.apk.check_min_version(args, args.suffix)
-            pmb.chroot.root(args, args.command, args.suffix, log=False)
-        elif args.action == "index":
-            pmb.build.index_repo(args)
-        elif args.action == "initfs":
-            pmb.chroot.initfs.frontend(args)
-        elif args.action == "install":
-            pmb.install.install(args)
-        elif args.action == "flasher":
-            pmb.flasher.frontend(args)
-        elif args.action == "menuconfig":
-            pmb.build.menuconfig(args, args.package, args.deviceinfo["arch"])
-        elif args.action == "parse_apkbuild":
-            print(json.dumps(pmb.parse.apkbuild(args, args.aports + "/" +
-                                                args.package + "/APKBUILD"), indent=4))
-        elif args.action == "parse_apkindex":
-            print(
-                json.dumps(
-                    pmb.parse.apkindex.parse(
-                        args,
-                        args.apkindex_path),
-                    indent=4))
-        elif args.action == "shutdown":
-            pmb.chroot.shutdown(args)
-        elif args.action == "stats":
-            pmb.build.ccache_stats(args, args.arch)
-        elif args.action == "log":
-            pmb.helpers.run.user(args, ["tail", "-f", args.log,
-                                        "-n", args.lines], log=False)
-        elif args.action == "log_distccd":
-            pmb.chroot.user(args, ["tail", "-f", "/home/user/distccd.log",
-                                   "-n", args.lines], log=False)
-        elif args.action == "zap":
-            pmb.chroot.zap(args)
+        # If an action_xxx function is defined in local scope, run it with args
+        func = locals().get('action_' + args.action)
+        if func:
+            func(args)
         else:
             logging.info("Run pmbootstrap -h for usage information.")