feat(mappers): Stream name can now be accessed in stream maps

docs/stream_maps.md

@@ -228,30 +228,29 @@ can be referenced directly by mapping expressions.
 
 #### Built-In Functions
 
-- [`md5()`](inv:python:py:module:#hashlib) - returns an inline MD5 hash of any string, outputting
-    the string representation of the hash's hex digest.
-  - This is defined by the SDK internally with native python:
-    [`hashlib.md5(<input>.encode("utf-8")).hexdigest()`](inv:python:py:method:#hashlib.hash.hexdigest).
-- [`datetime`](inv:python:py:module:#datetime) - This is the datetime module object from the Python
-    standard library. You can access [`datetime.datetime`](inv:python:py:class:#datetime.datetime),
-    [`datetime.timedelta`](inv:python:py:class:#datetime.timedelta), etc.
-- [`json`](inv:python:py:module:#json) - This is the json module object from the Python standard
-    library. Primarily used for calling [`json.dumps()`](inv:python:py:function:#json.dumps)
-    and [`json.loads()`](inv:python:py:function:#json.loads).
+The following functions and namespaces are available for use in mapping expressions:
+
+| Function                                     | Description                                                                                                                                                                                                                                                            |
+| :------------------------------------------- | :--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| [`md5()`](inv:python:py:module:#hashlib)     | Returns an inline MD5 hash of any string, outputting the string representation of the hash's hex digest. This is defined by the SDK internally with native python: [`hashlib.md5(<input>.encode("utf-8")).hexdigest()`](inv:python:py:method:#hashlib.hash.hexdigest). |
+| [`datetime`](inv:python:py:module:#datetime) | This is the datetime module object from the Python standard library. You can access [`datetime.datetime`](inv:python:py:class:#datetime.datetime), [`datetime.timedelta`](inv:python:py:class:#datetime.timedelta), etc.                                               |
+| [`json`](inv:python:py:module:#json)         | This is the json module object from the Python standard library. Primarily used for calling [`json.dumps()`](inv:python:py:function:#json.dumps) and [`json.loads()`](inv:python:py:function:#json.loads).                                                             |
 
 #### Built-in Variable Names
 
-- `config` - a dictionary with the `stream_map_config` values from settings. This can be used
-  to provide a secret hash seed, for instance.
-- `record` - an alias for the record values dictionary in the current stream.
-- `_` - same as `record` but shorter to type
-- `self` - the existing property value if the property already exists
-- `fake` - a [`Faker`](inv:faker:std:doc#index) instance, configurable via `faker_config`
-  (see previous example) - see the built-in [standard providers](inv:faker:std:doc#providers)
-  for available methods
+The following variables are available in the context of a mapping expression:
+
+| Variable          | Description                                                                                                                                                                                       |
+| :---------------- | :------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
+| `config`          | A dictionary with the `stream_map_config` values from settings. This can be used to provide a secret hash seed, for instance.                                                                     |
+| `record`          | An alias for the record values dictionary in the current stream.                                                                                                                                  |
+| `_`               | Same as `record` but shorter to type.                                                                                                                                                             |
+| `self`            | The existing property value if the property already exists.                                                                                                                                       |
+| `fake`            | A [`Faker`](inv:faker:std:doc#index) instance, configurable via `faker_config` (see previous example) - see the built-in [standard providers](inv:faker:std:doc#providers) for available methods. |
+| `__stream_name__` | The name of the stream. Useful when [applying the same transformation to multiple streams](#applying-a-mapping-across-two-or-more-streams).                                                       |
 
   ```{tip}
-  The `fake` object is only available if the plugin specifies `faker` as an additional dependency (through the `singer-sdk` `faker` extra, or directly).
+  To use the `fake` object, the `faker` library must be installed.
   ```
 
 :::{versionadded} 0.35.0
@@ -266,10 +265,17 @@ The `Faker` class.
 The `Faker` class was deprecated in favor of instance methods on the `fake` object.
 :::
 
+:::{versionadded} 0.42.0
+The `__stream_name__` variable.
+:::
+
 #### Built-in Alias Variable Names
 
 The following variables are available in the context of the `__alias__` expression:
-- `__stream_name__` - the existing stream name
+
+| Variable          | Description              |
+| :---------------- | :----------------------- |
+| `__stream_name__` | The existing stream name |
 
 :::{versionadded} 0.42.0
 The `__stream_name__` variable.

singer_sdk/mapper.py

@@ -337,6 +337,7 @@ def _eval(
         names["_"] = record  # Add a shorthand alias in case of reserved words in names
         names["record"] = record  # ...and a longhand alias
         names["config"] = self.map_config  # Allow map config access within transform
+        names["__stream_name__"] = self.stream_alias  # Access stream name in transform
 
         if self.fake:
             from faker import Faker  # noqa: PLC0415

tests/core/test_mapper.py

@@ -780,6 +780,12 @@ def discover_streams(self):
             "aliased_stream_quoted.jsonl",
             id="aliased_stream_quoted",
         ),
+        pytest.param(
+            {"mystream": {"source_table": "__stream_name__"}},
+            {"flattening_enabled": False, "flattening_max_depth": 0},
+            "builtin_variable_stream_name.jsonl",
+            id="builtin_variable_stream_name",
+        ),
         pytest.param(
             {"mystream": {"__alias__": "'aliased_' + __stream_name__"}},
             {"flattening_enabled": False, "flattening_max_depth": 0},
@@ -792,6 +798,28 @@ def discover_streams(self):
             "builtin_variable_stream_name_alias_expr.jsonl",
             id="builtin_variable_stream_name_alias_expr",
         ),
+        pytest.param(
+            {
+                "mystream": {
+                    "email": "self.upper()",
+                    "__else__": None,
+                }
+            },
+            {"flattening_enabled": False, "flattening_max_depth": 0},
+            "builtin_variable_self.jsonl",
+            id="builtin_variable_self",
+        ),
+        pytest.param(
+            {
+                "mystream": {
+                    "email": "_['email'].upper()",
+                    "__else__": None,
+                }
+            },
+            {"flattening_enabled": False, "flattening_max_depth": 0},
+            "builtin_variable_underscore.jsonl",
+            id="builtin_variable_underscore",
+        ),
         pytest.param(
             {},
             {"flattening_enabled": True, "flattening_max_depth": 0},

tests/snapshots/mapped_stream/builtin_variable_self.jsonl

@@ -0,0 +1,6 @@
+{"type":"STATE","value":{}}
+{"type":"SCHEMA","stream":"mystream","schema":{"type":"object","properties":{"email":{"type":["string","null"]}}},"key_properties":[]}
+{"type":"RECORD","stream":"mystream","record":{"email":"ALICE@EXAMPLE.COM"},"time_extracted":"2022-01-01T00:00:00+00:00"}
+{"type":"RECORD","stream":"mystream","record":{"email":"BOB@EXAMPLE.COM"},"time_extracted":"2022-01-01T00:00:00+00:00"}
+{"type":"RECORD","stream":"mystream","record":{"email":"CHARLIE@EXAMPLE.COM"},"time_extracted":"2022-01-01T00:00:00+00:00"}
+{"type":"STATE","value":{"bookmarks":{"mystream":{}}}}

tests/snapshots/mapped_stream/builtin_variable_stream_name.jsonl

@@ -0,0 +1,6 @@
+{"type":"STATE","value":{}}
+{"type":"SCHEMA","stream":"mystream","schema":{"properties":{"email":{"type":["string"]},"count":{"type":["integer","null"]},"user":{"properties":{"id":{"type":["integer","null"]},"sub":{"properties":{"num":{"type":["integer","null"]},"custom_obj":{"type":["string","null"]}},"type":["object","null"]},"some_numbers":{"items":{"type":["number"]},"type":["array","null"]}},"type":["object","null"]},"source_table":{"type":["string","null"]}},"type":"object","required":["email"]},"key_properties":[]}
+{"type":"RECORD","stream":"mystream","record":{"email":"alice@example.com","count":21,"user":{"id":1,"sub":{"num":1,"custom_obj":"obj-hello"},"some_numbers":[3.14,2.718]},"source_table":"mystream"},"time_extracted":"2022-01-01T00:00:00+00:00"}
+{"type":"RECORD","stream":"mystream","record":{"email":"bob@example.com","count":13,"user":{"id":2,"sub":{"num":2,"custom_obj":"obj-world"},"some_numbers":[10.32,1.618]},"source_table":"mystream"},"time_extracted":"2022-01-01T00:00:00+00:00"}
+{"type":"RECORD","stream":"mystream","record":{"email":"charlie@example.com","count":19,"user":{"id":3,"sub":{"num":3,"custom_obj":"obj-hello"},"some_numbers":[1.414,1.732]},"source_table":"mystream"},"time_extracted":"2022-01-01T00:00:00+00:00"}
+{"type":"STATE","value":{"bookmarks":{"mystream":{}}}}

tests/snapshots/mapped_stream/builtin_variable_underscore.jsonl

@@ -0,0 +1,6 @@
+{"type":"STATE","value":{}}
+{"type":"SCHEMA","stream":"mystream","schema":{"type":"object","properties":{"email":{"type":["string","null"]}}},"key_properties":[]}
+{"type":"RECORD","stream":"mystream","record":{"email":"ALICE@EXAMPLE.COM"},"time_extracted":"2022-01-01T00:00:00+00:00"}
+{"type":"RECORD","stream":"mystream","record":{"email":"BOB@EXAMPLE.COM"},"time_extracted":"2022-01-01T00:00:00+00:00"}
+{"type":"RECORD","stream":"mystream","record":{"email":"CHARLIE@EXAMPLE.COM"},"time_extracted":"2022-01-01T00:00:00+00:00"}
+{"type":"STATE","value":{"bookmarks":{"mystream":{}}}}