form definition dictionary keys must be the field names now; refactoring in the Form class

src/yamlhttpforms/form.py

@@ -69,6 +69,29 @@ class FormField:
 
 
 class Form:
+
+    @staticmethod
+    def fields_from_dict(definition: Dict[str, Optional[dict]]) -> Dict[str, FormField]:
+        """
+        Takes a dictionary defining form fields and creates `FormFields` objects from it.
+        Every key in `definition` is interpreted as the field's name.
+        The corresponding value can be `None` or a dictionary that can be unpacked into the FormField constructor call
+        alongside the name.
+        The special key `alias` in a field's dictionary is also allowed. If it is present, the corresponding value
+        will be used as the key in the output dictionary; otherwise the field's name is used as the key.
+        The constructed `FormField` objects are the values in the output dictionary.
+        """
+        field_dict = {}
+        for name, field_def in definition.items():
+            if field_def is None:
+                field_def = {}
+            if isinstance(field_def, dict):
+                alias = field_def.pop('alias', name)
+                field_dict[alias] = FormField(name, **field_def)
+            else:
+                raise TypeError("Field definitions must be either dictionaries or `None`")
+        return field_dict
+
     def __init__(self, definition: Dict[str, Dict], full_payload: bool = True, url: str = None):
         """
         Creates a form instance from a definition dictionary. Each element in the dictionary must define a field.
@@ -85,7 +108,7 @@ class Form:
             url (optional):
                 Can be set in advance to the url that requests using this form's payload should be made to.
         """
-        self.fields: Dict[str, FormField] = {alias: FormField(**field_def) for alias, field_def in definition.items()}
+        self.fields: Dict[str, FormField] = self.fields_from_dict(definition)
         self.full_payload_always: bool = full_payload
         self.url: Optional[str] = url
 
@@ -107,8 +130,10 @@ class Form:
 
         Args:
             kwargs (optional):
-                Every key must correspond to a key in the internal dictionary of fields;
+                Every key must correspond to an alias or name of a field in the internal dictionary of fields;
                 otherwise that key-value-pair is ignored.
+                If both a field's alias and name are different and both are present as keys in `kwargs`,
+                the alias-key takes precedence.
                 Values will be passed into the payload (if they pass validation).
                 Select fields with predefined options will only allow one of the options to be passed.
                 If `None` is passed as a value, the corresponding field's default value will be used in the payload.
@@ -117,15 +142,15 @@ class Form:
             Validated name-value-mapping to be used for HTTP requests from the form's fields.
         """
         payload = {}
-        for key, field in self.fields.items():
-            if key in kwargs.keys():
-                value = kwargs[key]
-                if value is None:
-                    payload[field.name] = field.default
-                else:
-                    payload[field.name] = field.clean(value)
+        for alias, field in self.fields.items():
+            if alias in kwargs.keys():
+                value = kwargs[alias]
+                payload[field.name] = field.default if value is None else field.clean(value)
+            elif alias != field.name and field.name in kwargs.keys():
+                value = kwargs[field.name]
+                payload[field.name] = field.default if value is None else field.clean(value)
             elif field.required:
-                raise ValueError(f"`{key}` is a required field, but no argument was passed.")
+                raise ValueError(f"`{alias}` is a required field, but no argument was passed.")
             elif self.full_payload_always:
                 payload[field.name] = field.default
         return payload