Make error messages more user friendly

README.rst

@@ -44,7 +44,7 @@ To initialize it, you have to provide:
 .. code-block:: python
 
     import wikipediaapi
-    wiki_wiki = wikipediaapi.Wikipedia('MyProjectName (merlin@example.com)', 'en')
+    wiki_wiki = wikipediaapi.Wikipedia(user_agent='MyProjectName (merlin@example.com)', language='en')
 
     page_py = wiki_wiki.page('Python_(programming_language)')
 

example.py

@@ -7,7 +7,7 @@
 
 user_agent = "Wikipedia-API Example (merlin@example.com)"
 
-wiki_wiki = wikipediaapi.Wikipedia(user_agent, "en")
+wiki_wiki = wikipediaapi.Wikipedia(user_agent=user_agent, language="en")
 
 page_py = wiki_wiki.page("Python_(programming_language)")
 
@@ -89,7 +89,7 @@ def print_categories(page):
 print("Page - Summary: %s" % page_nonexisting.summary[0:60])
 
 
-wiki_de = wikipediaapi.Wikipedia(user_agent, "de")
+wiki_de = wikipediaapi.Wikipedia(user_agent=user_agent, language="de")
 de_page = wiki_de.page("Deutsche Sprache")
 print(de_page.title + ": " + de_page.fullurl)
 print(de_page.summary[0:60])
@@ -110,7 +110,7 @@ def print_categorymembers(categorymembers, level=0, max_level=2):
 print("Category members: Category:Physics")
 print_categorymembers(cat.categorymembers, max_level=1)
 
-wiki_hi = wikipediaapi.Wikipedia(user_agent, "hi")
+wiki_hi = wikipediaapi.Wikipedia(user_agent=user_agent, language="hi")
 # fetch page about Python in Hindu
 # https://hi.wikipedia.org/wiki/%E0%A4%AA%E0%A4%BE%E0%A4%87%E0%A4%A5%E0%A4%A8
 
@@ -122,28 +122,34 @@ def print_categorymembers(categorymembers, level=0, max_level=2):
 print(p_hi_python_quoted.summary[0:60])
 
 # Fetch page about Python in Chinese
-wiki_zh = wikipediaapi.Wikipedia(user_agent, "zh")
+wiki_zh = wikipediaapi.Wikipedia(user_agent=user_agent, language="zh")
 zh_page = wiki_zh.page("Python")
 print(zh_page.title + ": " + zh_page.fullurl)
 print(zh_page.summary[0:60])
 print(repr(zh_page.varianttitles))
 
 # https://zh.wikipedia.org/zh-cn/Python
-wiki_zh_cn = wikipediaapi.Wikipedia(user_agent, "zh", "zh-cn")
+wiki_zh_cn = wikipediaapi.Wikipedia(
+    user_agent=user_agent, language="zh", variant="zh-cn"
+)
 zh_page_cn = wiki_zh_cn.page("Python")
 print(zh_page_cn.title + ": " + zh_page_cn.fullurl)
 print(zh_page_cn.summary[0:60])
 print(repr(zh_page_cn.varianttitles))
 
 # https://zh.wikipedia.org/zh-tw/Python
-wiki_zh_tw = wikipediaapi.Wikipedia(user_agent, "zh", "zh-tw")
+wiki_zh_tw = wikipediaapi.Wikipedia(
+    user_agent=user_agent, language="zh", variant="zh-tw"
+)
 zh_page_tw = wiki_zh_tw.page("Python")
 print(zh_page_tw.title + ": " + zh_page_tw.fullurl)
 print(zh_page_tw.summary[0:60])
 print(repr(zh_page_tw.varianttitles))
 
 # https://zh.wikipedia.org/zh-sg/Python
-wiki_zh_sg = wikipediaapi.Wikipedia(user_agent, "zh", "zh-sg")
+wiki_zh_sg = wikipediaapi.Wikipedia(
+    user_agent=user_agent, language="zh", variant="zh-sg"
+)
 zh_page_sg = wiki_zh_sg.page("Python")
 print(zh_page_sg.title + ": " + zh_page_sg.fullurl)
 print(zh_page_sg.summary[0:60])

tests/wikipedia_test.py

@@ -13,11 +13,63 @@ def test_missing_user_agent_should_fail(self):
                 AssertionError(
                     "Please, be nice to Wikipedia and specify user agent - "
                     + "https://meta.wikimedia.org/wiki/User-Agent_policy. "
-                    + "Current user_agent: 'en' is not sufficient."
+                    + "Current user_agent: 'en' is not sufficient. "
+                    + "Use Wikipedia(user_agent='your-user-agent', language='en')"
                 )
             ),
         )
 
+    def test_swapped_parameters_in_constructor(self):
+        with self.assertRaises(AssertionError) as e:
+            wikipediaapi.Wikipedia("en", "my-user-agent")
+        self.assertEqual(
+            str(e.exception),
+            str(
+                AssertionError(
+                    "Please, be nice to Wikipedia and specify user agent - "
+                    + "https://meta.wikimedia.org/wiki/User-Agent_policy. "
+                    + "Current user_agent: 'en' is not sufficient. "
+                    + "Use Wikipedia(user_agent='your-user-agent', language='en')"
+                )
+            ),
+        )
+
+    def test_empty_parameters_in_constructor(self):
+        with self.assertRaises(AssertionError) as e:
+            wikipediaapi.Wikipedia("", "")
+        self.assertEqual(
+            str(e.exception),
+            str(
+                AssertionError(
+                    "Please, be nice to Wikipedia and specify user agent - "
+                    + "https://meta.wikimedia.org/wiki/User-Agent_policy. "
+                    + "Current user_agent: '' is not sufficient. "
+                    + "Use Wikipedia(user_agent='your-user-agent', language='your-language')"
+                )
+            ),
+        )
+
+    def test_empty_language_in_constructor(self):
+        with self.assertRaises(AssertionError) as e:
+            wikipediaapi.Wikipedia("test-user-agent", "")
+        self.assertEqual(
+            str(e.exception),
+            str(
+                AssertionError(
+                    "Specify language. Current language: '' is not sufficient. "
+                    + "Use Wikipedia(user_agent='test-user-agent', language='your-language')"
+                )
+            ),
+        )
+
+    def test_long_language_and_user_agent(self):
+        wiki = wikipediaapi.Wikipedia(
+            user_agent="param-user-agent", language="very-long-language"
+        )
+        self.assertIsNotNone(wiki)
+        self.assertEqual(wiki.language, "very-long-language")
+        self.assertIsNone(wiki.variant)
+
     def test_user_agent_is_used(self):
         wiki = wikipediaapi.Wikipedia(
             user_agent="param-user-agent",
@@ -28,6 +80,7 @@ def test_user_agent_is_used(self):
             user_agent,
             "param-user-agent (" + wikipediaapi.USER_AGENT + ")",
         )
+        self.assertEqual(wiki.language, "en")
 
     def test_user_agent_in_headers_is_fine(self):
         wiki = wikipediaapi.Wikipedia(

wikipediaapi/__init__.py

@@ -23,6 +23,9 @@
     + "; https://github.com/martin-majlis/Wikipedia-API/"
 )
 
+MIN_USER_AGENT_LEN = 5
+MAX_LANG_LEN = 5
+
 log = logging.getLogger(__name__)
 
 
@@ -163,29 +166,21 @@ def __init__(
         request_kwargs.setdefault("timeout", 10.0)
 
         default_headers = {} if headers is None else headers
-        if user_agent:
+        if user_agent is not None:
             default_headers.setdefault(
                 "User-Agent",
                 user_agent,
             )
-        used_user_agent = default_headers.get("User-Agent")
-        if not (used_user_agent and len(used_user_agent) > 5):
-            raise AssertionError(
-                "Please, be nice to Wikipedia and specify user agent - "
-                + "https://meta.wikimedia.org/wiki/User-Agent_policy. Current user_agent: '"
-                + str(used_user_agent)
-                + "' is not sufficient."
-            )
-        default_headers["User-Agent"] += " (" + USER_AGENT + ")"
+        used_language, used_variant, used_user_agent = self._check_and_correct_params(
+            language,
+            variant,
+            default_headers.get("User-Agent"),
+        )
 
-        self.language = language.strip().lower()
-        if not self.language:
-            raise AssertionError(
-                "Specify language. Current language: '"
-                + str(self.language)
-                + "' is not sufficient."
-            )
-        self.variant = variant.strip().lower() if variant else variant
+        default_headers["User-Agent"] = used_user_agent + " (" + USER_AGENT + ")"
+
+        self.language = used_language
+        self.variant = used_variant
         self.extract_format = extract_format
 
         log.info(
@@ -722,6 +717,53 @@ def _common_attributes(extract, page: "WikipediaPage"):
             if attr in extract:
                 page._attributes[attr] = extract[attr]
 
+    @staticmethod
+    def _check_and_correct_params(
+        language: Optional[str], variant: Optional[str], user_agent: Optional[str]
+    ) -> tuple[str, Optional[str], str]:
+        """
+        Checks the constructor parameters and throws AssertionError if they are incorrect.
+        Otherwise, it normalises them to easy use later on.
+        :param language: Language mutation of Wikipedia
+        :param variant: Language variant
+        :param user_agent: HTTP User-Agent used in requests
+        :return: tuple of language, variant, user_agent
+        """
+        if not user_agent or len(user_agent) < MIN_USER_AGENT_LEN:
+            raise AssertionError(
+                "Please, be nice to Wikipedia and specify user agent - "
+                + "https://meta.wikimedia.org/wiki/User-Agent_policy. Current user_agent: '"
+                + str(user_agent)
+                + "' is not sufficient. "
+                + "Use Wikipedia(user_agent='your-user-agent', language='"
+                + (str(user_agent) or "your-language")
+                + "')"
+            )
+
+        if not language:
+            raise AssertionError(
+                "Specify language. Current language: '"
+                + str(language)
+                + "' is not sufficient. "
+                + "Use Wikipedia(user_agent='"
+                + str(user_agent)
+                + "', language='your-language')"
+            )
+
+        used_language = language.strip().lower()
+        if len(used_language) > MAX_LANG_LEN:
+            log.warning(
+                "Used language '%s' is longer than %d. It is suspicious",
+                used_language,
+                MAX_LANG_LEN,
+            )
+
+        return (
+            used_language,
+            variant.strip().lower() if variant else variant,
+            user_agent,
+        )
+
 
 class WikipediaPageSection:
     """WikipediaPageSection represents section in the page."""