Correct handling of boolean selections

The selections proxy class, which mashes together command-line
arguments and configuration options, contained a longstanding and
fatal flaw with its handling of boolean values. In particular,
falsey values were consistently treated as truthy due to naively
recasting str to bool (which will always yield True unless empty).
This went unnoticed for so long because the majority of these
settings default to False, meaning the only reason most users had to
set them was to override them to True.

Many thanks to Jordan Russell for bringing this bug to my attention,
and for supplying an initial patch on which this fix is heavily
based.

Co-Authored-By: Jordan Russell

weather.py

@@ -95,7 +95,19 @@ class Selections:
         return None
     def get_bool(self, option, argument=None):
         """Get data and coerce to a boolean if necessary."""
-        return bool(self.get(option, argument))
+        # Mimic configparser's getboolean() method by treating
+        # false/no/off/0 as False and true/yes/on/1 as True values,
+        # case-insensitively
+        value = self.get(option, argument)
+        if isinstance(value, bool):
+            return value
+        if isinstance(value, str):
+            vlower = value.lower()
+            if vlower in ('false', 'no', 'off', '0'):
+                return False
+            elif vlower in ('true', 'yes', 'on', '1'):
+                return True
+        raise ValueError("Not a boolean: %s" % value)
     def getint(self, option, argument=None):
         """Get data and coerce to an integer if necessary."""
         value = self.get(option, argument)
@@ -365,7 +377,7 @@ def get_options(config):
 
     # the -a/--alert option
     if config.has_option("default", "alert"):
-        default_alert = bool(config.get("default", "alert"))
+        default_alert = config.getboolean("default", "alert")
     else: default_alert = False
     option_parser.add_option("-a", "--alert",
         dest="alert",
@@ -420,7 +432,7 @@ def get_options(config):
 
     # the -f/--forecast option
     if config.has_option("default", "forecast"):
-        default_forecast = bool(config.get("default", "forecast"))
+        default_forecast = config.getboolean("default", "forecast")
     else: default_forecast = False
     option_parser.add_option("-f", "--forecast",
         dest="forecast",
@@ -448,7 +460,7 @@ def get_options(config):
 
     # the --imperial option
     if config.has_option("default", "imperial"):
-        default_imperial = bool(config.get("default", "imperial"))
+        default_imperial = config.getboolean("default", "imperial")
     else: default_imperial = False
     option_parser.add_option("--imperial",
         dest="imperial",
@@ -479,7 +491,7 @@ def get_options(config):
 
     # the -m/--metric option
     if config.has_option("default", "metric"):
-        default_metric = bool(config.get("default", "metric"))
+        default_metric = config.getboolean("default", "metric")
     else: default_metric = False
     option_parser.add_option("-m", "--metric",
         dest="metric",
@@ -489,7 +501,7 @@ def get_options(config):
 
     # the -n/--no-conditions option
     if config.has_option("default", "conditions"):
-        default_conditions = bool(config.get("default", "conditions"))
+        default_conditions = config.getboolean("default", "conditions")
     else: default_conditions = True
     option_parser.add_option("-n", "--no-conditions",
         dest="conditions",
@@ -499,7 +511,7 @@ def get_options(config):
 
     # the --no-cache option
     if config.has_option("default", "cache"):
-        default_cache = bool(config.get("default", "cache"))
+        default_cache = config.getboolean("default", "cache")
     else: default_cache = True
     option_parser.add_option("--no-cache",
         dest="cache",
@@ -509,7 +521,7 @@ def get_options(config):
 
     # the --no-cache-data option
     if config.has_option("default", "cache_data"):
-        default_cache_data = bool(config.get("default", "cache_data"))
+        default_cache_data = config.getboolean("default", "cache_data")
     else: default_cache_data = True
     option_parser.add_option("--no-cache-data",
         dest="cache_data",
@@ -519,7 +531,7 @@ def get_options(config):
 
     # the --no-cache-search option
     if config.has_option("default", "cache_search"):
-        default_cache_search = bool(config.get("default", "cache_search"))
+        default_cache_search = config.getboolean("default", "cache_search")
     else: default_cache_search = True
     option_parser.add_option("--no-cache-search",
         dest="cache_search",
@@ -529,7 +541,7 @@ def get_options(config):
 
     # the -q/--quiet option
     if config.has_option("default", "quiet"):
-        default_quiet = bool(config.get("default", "quiet"))
+        default_quiet = config.getboolean("default", "quiet")
     else: default_quiet = False
     option_parser.add_option("-q", "--quiet",
         dest="quiet",
@@ -548,7 +560,7 @@ def get_options(config):
 
     # the -v/--verbose option
     if config.has_option("default", "verbose"):
-        default_verbose = bool(config.get("default", "verbose"))
+        default_verbose = config.getboolean("default", "verbose")
     else: default_verbose = False
     option_parser.add_option("-v", "--verbose",
         dest="verbose",