Add separate classes for API exceptions, raise error_for_code().

This makes the caller's life easier. They can catch
mega.errors.EFAILED instead of catching mega.errors.RequestError
and checking the message attribute.
Because these classes inherit from RequestError, and they have a code
and message attribute, anyone currently catching RequestError should
not have any backwards compatibility issues.
Furthermore, this fixes an existing issue in the codebase where
RequestError is raised with a custom string message, which was causing
IndexError since that message wasn't in CODE_TO_DESCRIPTIONS.

src/mega/__init__.py

@@ -1 +1,2 @@
 from .mega import Mega  # noqa
+from . import errors

src/mega/errors.py

@@ -5,83 +5,154 @@ class ValidationError(Exception):
     pass
 
 
-_CODE_TO_DESCRIPTIONS = {
-    -1: (
-        'EINTERNAL',
-        (
-            'An internal error has occurred. Please submit a bug report, '
-            'detailing the exact circumstances in which this error occurred'
-        )
-    ),
-    -2: ('EARGS', 'You have passed invalid arguments to this command'),
-    -3: (
-        'EAGAIN',
-        (
-            '(always at the request level) A temporary congestion or server '
-            'malfunction prevented your request from being processed. '
-            'No data was altered. Retry. Retries must be spaced with '
-            'exponential backoff'
-        )
-    ),
-    -4: (
-        'ERATELIMIT',
-        (
-            'You have exceeded your command weight per time quota. Please '
-            'wait a few seconds, then try again (this should never happen '
-            'in sane real-life applications)'
-        )
-    ),
-    -5: ('EFAILED', 'The upload failed. Please restart it from scratch'),
-    -6: (
-        'ETOOMANY',
-        'Too many concurrent IP addresses are accessing this upload target URL'
-    ),
-    -7: (
-        'ERANGE',
-        (
-            'The upload file packet is out of range or not starting and '
-            'ending on a chunk boundary'
-        )
-    ),
-    -8: (
-        'EEXPIRED',
-        (
-            'The upload target URL you are trying to access has expired. '
-            'Please request a fresh one'
-        )
-    ),
-    -9: ('ENOENT', 'Object (typically, node or user) not found'),
-    -10: ('ECIRCULAR', 'Circular linkage attempted'),
-    -11: (
-        'EACCESS',
-        'Access violation (e.g., trying to write to a read-only share)'
-    ),
-    -12: ('EEXIST', 'Trying to create an object that already exists'),
-    -13: ('EINCOMPLETE', 'Trying to access an incomplete resource'),
-    -14: ('EKEY', 'A decryption operation failed (never returned by the API)'),
-    -15: ('ESID', 'Invalid or expired user session, please relogin'),
-    -16: ('EBLOCKED', 'User blocked'),
-    -17: ('EOVERQUOTA', 'Request over quota'),
-    -18: (
-        'ETEMPUNAVAIL',
-        'Resource temporarily not available, please try again later'
-    ),
-    -19: ('ETOOMANYCONNECTIONS', 'many connections on this resource'),
-    -20: ('EWRITE', 'Write failed'),
-    -21: ('EREAD', 'Read failed'),
-    -22: ('EAPPKEY', 'Invalid application key; request not processed'),
-}
-
-
 class RequestError(Exception):
     """
     Error in API request
     """
-    def __init__(self, message):
+    def __init__(self, message=None):
-        code = message
+        # If you need to raise a generic RequestError with a custom message,
-        self.code = code
+        # use this constructor. Otherwise you can use error_for_code.
-        code_desc, long_desc = _CODE_TO_DESCRIPTIONS[code]
+        if message is not None:
-        self.message = f'{code_desc}, {long_desc}'
+            self.message = message
 
     def __str__(self):
         return self.message
+
+
+class EINTERNAL(RequestError):
+    code = -1
+    message = (
+        'An internal error has occurred. Please submit a bug report, detailing '
+        'the exact circumstances in which this error occurred'
+    )
+
+class EARGS(RequestError):
+    code = -2
+    message = 'You have passed invalid arguments to this command'
+
+class EAGAIN(RequestError):
+    code = -3
+    message = (
+        '(always at the request level) A temporary congestion or server '
+        'malfunction prevented your request from being processed. No data was '
+        'altered. Retry. Retries must be spaced with exponential backoff'
+    )
+
+class ERATELIMIT(RequestError):
+    code = -4
+    message = (
+        'You have exceeded your command weight per time quota. Please wait a '
+        'few seconds, then try again (this should never happen in sane '
+        'real-life applications)'
+    )
+
+class EFAILED(RequestError):
+    code = -5
+    message = 'The upload failed. Please restart it from scratch'
+
+class ETOOMANY(RequestError):
+    code = -6
+    message = (
+        'Too many concurrent IP addresses are accessing this upload target URL'
+    )
+
+class ERANGE(RequestError):
+    code = -7
+    message = (
+        'The upload file packet is out of range or not starting and ending on '
+        'a chunk boundary'
+    )
+
+class EEXPIRED(RequestError):
+    code = -8
+    message = (
+        'The upload target URL you are trying to access has expired. Please '
+        'request a fresh one'
+    )
+
+class ENOENT(RequestError):
+    code = -9
+    message = 'Object (typically, node or user) not found'
+
+class ECIRCULAR(RequestError):
+    code = -10
+    message = 'Circular linkage attempted'
+
+class EACCESS(RequestError):
+    code = -11
+    message = 'Access violation (e.g., trying to write to a read-only share)'
+
+class EEXIST(RequestError):
+    code = -12
+    message = 'Trying to create an object that already exists'
+
+class EINCOMPLETE(RequestError):
+    code = -13
+    message = 'Trying to access an incomplete resource'
+
+class EKEY(RequestError):
+    code = -14
+    message = 'A decryption operation failed (never returned by the API)'
+
+class ESID(RequestError):
+    code = -15
+    message = 'Invalid or expired user session, please relogin'
+
+class EBLOCKED(RequestError):
+    code = -16
+    message = 'User blocked'
+
+class EOVERQUOTA(RequestError):
+    code = -17
+    message = 'Request over quota'
+
+class ETEMPUNAVAIL(RequestError):
+    code = -18
+    message = 'Resource temporarily not available, please try again later'
+
+class ETOOMANYCONNECTIONS(RequestError):
+    code = -19
+    message = 'many connections on this resource'
+
+class EWRITE(RequestError):
+    code = -20
+    message = 'Write failed'
+
+class EREAD(RequestError):
+    code = -21
+    message = 'Read failed'
+
+class EAPPKEY(RequestError):
+    code = -22
+    message = 'Invalid application key; request not processed'
+
+
+_CODE_TO_CLASSES = {
+    -1: EINTERNAL,
+    -2: EARGS,
+    -3: EAGAIN,
+    -4: ERATELIMIT,
+    -5: EFAILED,
+    -6: ETOOMANY,
+    -7: ERANGE,
+    -8: EEXPIRED,
+    -9: ENOENT,
+    -10: ECIRCULAR,
+    -11: EACCESS,
+    -12: EEXIST,
+    -13: EINCOMPLETE,
+    -14: EKEY,
+    -15: ESID,
+    -16: EBLOCKED,
+    -17: EOVERQUOTA,
+    -18: ETEMPUNAVAIL,
+    -19: ETOOMANYCONNECTIONS,
+    -20: EWRITE,
+    -21: EREAD,
+    -22: EAPPKEY,
+}
+
+
+def error_for_code(code):
+    cls = _CODE_TO_CLASSES[code]
+    return cls()

src/mega/mega.py

@@ -17,7 +17,7 @@ import shutil
 import requests
 from tenacity import retry, wait_exponential, retry_if_exception_type
 
-from .errors import ValidationError, RequestError
+from .errors import ValidationError, RequestError, error_for_code
 from .crypto import (
     a32_to_base64, encrypt_key, base64_url_encode, encrypt_attr, base64_to_a32,
     base64_url_decode, decrypt_attr, a32_to_str, get_chunks, str_to_a32,
@@ -186,7 +186,7 @@ class Mega:
                 msg = 'Request failed, retrying'
                 logger.info(msg)
                 raise RuntimeError(msg)
-            raise RequestError(json_resp)
+            raise error_for_code(json_resp)
         return json_resp[0]
 
     def _parse_url(self, url):