Add schema reducer and cover it with tests

package/schemas/__private/modify/schema_reducer.py

+from schemas.__private.fundamental_schemas import Array, ArrayStrict, Map, Schema
+from schemas.__private.custom_schemas import ApiOperationObject, Proposal
+from .local_tools import get_schema
+
+
+def get_schema_to_reduce(source: Schema, path: str):
+    # Remove last element from path, we don't want to get schema that will be deleted. We want to get box which holds
+    # this element.
+    try:
+        path = path[:path.rindex('.')]
+    except ValueError:
+        path = 'source'
+    schema_to_reduce = get_schema(source, path)
+    return schema_to_reduce
+
+
+def remove_schema_from_map(source: Schema, *, path: str = 'source'):
+    key_to_delete = path.split('.')[-1]
+    schema_to_reduce = get_schema_to_reduce(source, path)
+    assert isinstance(schema_to_reduce, (Map, ApiOperationObject, Proposal)), 'You are trying to remove schema from' \
+                                                                              ' object which is not a Map, ' \
+                                                                              'ApiOperationObject or Proposal.'
+    del schema_to_reduce[key_to_delete]
+
+
+def remove_schema_from_array(source: Schema, *, path: str = 'source'):
+    index_to_delete = int(path.split('.')[-1])
+    schema_to_reduce = get_schema_to_reduce(source, path)
+    assert isinstance(schema_to_reduce, (Array, ArrayStrict)), 'You are trying to remove schema from object which ' \
+                                                               'is not an Array or ArrayStrict'
+
+    del schema_to_reduce[index_to_delete]

tests/test_schema_modification.py

 from schemas.__private.modify.schema_expander import add_schema_to_array, add_schema_to_map
+from schemas.__private.modify.schema_reducer import remove_schema_from_map, remove_schema_from_array
 from schemas.predefined import *
 
 
@@ -108,3 +109,74 @@ def test_single_addition_to_array_nested_in_different_types():
         )
     )
 
+
+def test_single_deletion_in_outer_map():
+    schema = Map({'number': Int()})
+    remove_schema_from_map(schema, path='number')
+    assert schema == Map({})
+
+
+def test_single_deletion_in_inner_map():
+    schema = Map({
+        'inner_map': Map({
+            'id': Int()
+        })
+    })
+    remove_schema_from_map(schema, path='inner_map.id')
+
+    assert schema == Map({
+        'inner_map': Map({})
+    })
+
+
+def test_single_deletion_in_map_nested_in_different_types():
+    schema = Array(
+        ArrayStrict(
+            Map({
+                'values': AnyOf(
+                    Str(),
+                    Int(),
+                    Map({
+                        'key_to_delete': Str(),
+                    })
+                ),
+                'name': AccountName(),
+            })
+        )
+    )
+
+    remove_schema_from_map(schema, path='0.0.values.2.key_to_delete')
+
+    assert schema == Array(
+        ArrayStrict(
+            Map({
+                'values': AnyOf(
+                    Str(),
+                    Int(),
+                    Map({
+                    })
+                ),
+                'name': AccountName(),
+            })
+        )
+    )
+
+
+def test_single_deletion_in_outer_array():
+    schema = Array(Int(), Str())
+    remove_schema_from_array(schema, path='1')
+    assert schema == Array(Int())
+
+
+def test_single_deletion_in_inner_array():
+    schema = Array(
+        Array(
+            Hex(), Str(), Int(),
+        ))
+    remove_schema_from_array(schema, path='0.2')
+    assert schema == Array(
+        Array(
+            Hex(), Str(),
+        )
+    )
+