Assignment expression code optimization x 2.

This commit is the last in a commit chain significantly optimizing
generation of **assignment expressions** (i.e., PEP 572-compliant Python
expressions containing the ":=" walrus operator) throughout code
snippets dynamically generated by @beartype's type-checking code
generator. Since strings are expensive to repeatedly generate, @beartype
now internally caches and reuses frequently used local variables across
assignment expressions. In truth, this means nothing. But @leycec just
*had* to do this to satisfy his aberrant OCD disorder. I swear! It isn't
my fault! It's fast or it ain't @beartype. (*Holy bawling bowlers!*)

beartype/_check/checkmagic.py

@@ -152,7 +152,7 @@
 '''
 Substring prefixing all local variables providing a **pith** (i.e., either the
 current parameter or return value *or* item contained in the current parameter
-or return value being type-checked by the current call).
+or return value type-checked by the current call).
 '''
 
 

beartype/_check/code/codemake.py

@@ -26,7 +26,6 @@
 from beartype._check.checkmagic import (
     ARG_NAME_CLS_STACK,
     ARG_NAME_GETRANDBITS,
-    VAR_NAME_PITH_PREFIX,
     VAR_NAME_PITH_ROOT,
 )
 from beartype._check.code.codemagic import (
@@ -44,6 +43,7 @@
     add_func_scope_type_or_types,
     express_func_scope_type_ref,
 )
+from beartype._check.code.snip.codesnipcls import PITH_INDEX_TO_VAR_NAME
 from beartype._check.code.snip.codesnipstr import (
     CODE_HINT_CHILD_PLACEHOLDER_PREFIX,
     CODE_HINT_CHILD_PLACEHOLDER_SUFFIX,
@@ -507,14 +507,14 @@ class variable or method annotated by this hint *or* :data:`None`).
     #   effectively a leaf node with respect to performing this optimization.
 
     # Integer suffixing the name of each local variable assigned the value of
-    # the current pith in a Python >= 3.8-specific assignment expression, thus
-    # uniquifying this variable in the body of the current wrapper function.
+    # the current pith in a assignment expression, thus uniquifying this
+    # variable in the body of the current wrapper function.
     #
     # Note that this integer is intentionally incremented as an efficient
     # low-level scalar rather than as an inefficient high-level
     # "itertools.Counter" object. Since both are equally thread-safe in the
     # internal context of this function body, the former is preferable.
-    pith_curr_assign_expr_name_counter = 0
+    pith_curr_var_name_index = 0
 
     # Python >= 3.8-specific assignment expression assigning this full Python
     # expression to the local variable assigned the value of this expression.
@@ -1034,18 +1034,12 @@ def _enqueue_hint_child(pith_child_expr: str) -> str:
                 # and thus unnecessarily inefficient code.
                 if pith_curr_expr is not VAR_NAME_PITH_ROOT:
                     # Increment the integer suffixing the name of this variable
-                    # *BEFORE* defining this local variable.
-                    pith_curr_assign_expr_name_counter += 1
-
-                    #FIXME: Optimize away this inefficient string formatting
-                    #with an efficient dictionary lookup implemented similarly
-                    #to that of the "indent_curr" assignment, above.
-                    # Reduce the current pith expression to the name of this
-                    # local variable.
-                    pith_curr_var_name = (
-                        f'{VAR_NAME_PITH_PREFIX}'
-                        f'{pith_curr_assign_expr_name_counter}'
-                    )
+                    # *BEFORE* defining this variable.
+                    pith_curr_var_name_index += 1
+
+                    # Name of this local variable.
+                    pith_curr_var_name = PITH_INDEX_TO_VAR_NAME[
+                        pith_curr_var_name_index]
 
                     # Assignment expression assigning this full expression to
                     # this variable.

beartype/_check/code/snip/codesnipcls.py

@@ -13,4 +13,93 @@
 '''
 
 # ....................{ IMPORTS                            }....................
+from beartype._check.checkmagic import VAR_NAME_PITH_PREFIX
 
+# ....................{ SUBCLASSES                         }....................
+class PithIndexToVarName(dict):
+    '''
+    **Local pith variable name cache** (i.e., dictionary mapping from the
+    1-based index uniquely identifying each **pith** (i.e., current parameter or
+    return value *or* item contained in the current parameter or return value
+    type-checked by the current call in the body of a runtime type-checker
+    dynamically generated by :mod:`beartype`) to the corresponding name of a
+    prospective local variable assigned that value in that body).
+
+    See Also
+    --------
+    :data:`.PITH_INDEX_TO_VAR_NAME`
+        Singleton instance of this dictionary subclass.
+    '''
+
+    # ....................{ DUNDERS                        }....................
+    def __missing__(self, pith_index: int) -> str:
+        '''
+        Dunder method explicitly called by the superclass
+        :meth:`dict.__getitem__` method implicitly called on the first ``[``-
+        and ``]``-delimited attempt to access a local pith variable name
+        uniquely identified by the passed 1-based index.
+
+        Caveats
+        -------
+        **This method intentionally prohibits 0.** Why? Because the existing
+        :data:`beartype._check.checkmagic.VAR_NAME_PITH_ROOT` string global
+        already efficiently caches the local root pith variable name, which is
+        sufficiently common to warrant globalization.
+
+        Parameters
+        ----------
+        pith_index : int
+            1-based index suffixing the local pith variable name to be created,
+            cached, and returned.
+
+        Returns
+        -------
+        str
+            Prospective name of this local pith variable.
+
+        Raises
+        ------
+        AssertionError
+            If either:
+
+            * ``pith_level`` is *not* an integer.
+            * ``pith_level`` is a **non-positive integer** (i.e., is less than
+              or equal to 0).
+        '''
+        assert isinstance(pith_index, int), f'{repr(pith_index)} not integer.'
+        assert pith_index > 0, f'{pith_index} <= 0.'
+        # print(f'Generating indentation level {indent_level}...')
+
+        # Prospective name of this local pith variable.
+        pith_var_name = f'{VAR_NAME_PITH_PREFIX}{pith_index}'
+
+        # Cache this name.
+        self[pith_index] = pith_var_name
+
+        # Return this name.
+        return pith_var_name
+
+# ....................{ MAPPINGS                           }....................
+PITH_INDEX_TO_VAR_NAME = PithIndexToVarName()
+'''
+**Indentation cache singleton** (i.e., global dictionary efficiently mapping
+from 1-based indentation levels to the corresponding indentation string
+constant).
+
+Caveats
+-------
+**Indentation string constants should always be accessed via this cache rather
+than manually generated.** This cache dynamically creates and efficiently caches
+indentation string constants on the first access of those constants, obviating
+the performance cost of string formatting required to create these constants.
+
+Examples
+--------
+.. code-block:: pycon
+
+   >>> from beartype._check.code.snip.codesnipcls import PITH_INDEX_TO_VAR_NAME
+   >>> PITH_INDEX_TO_VAR_NAME[1]
+   '__beartype_pith_1'
+   >>> PITH_INDEX_TO_VAR_NAME[2]
+   '__beartype_pith_2'
+'''

beartype/_data/code/datacodeindent.py

@@ -50,8 +50,9 @@ def __missing__(self, indent_level: int) -> str:
             * ``indent_level`` is a **non-positive integer** (i.e., is less than
               or equal to 0).
         '''
-        assert isinstance(indent_level, int)
-        assert indent_level > 0
+        assert isinstance(indent_level, int), (
+            f'{repr(indent_level)} not integer.')
+        assert indent_level > 0, f'{indent_level} <= 0.'
         # print(f'Generating indentation level {indent_level}...')
 
         # String constant indented to this level of indentation.
@@ -67,8 +68,7 @@ def __missing__(self, indent_level: int) -> str:
         # Return this string constant.
         return indent_code
 
-# ....................{ DICTS                              }....................
-#FIXME: Unit test us up, please.
+# ....................{ MAPPINGS                           }....................
 INDENT_LEVEL_TO_CODE = IndentLevelToCode()
 '''
 **Indentation cache singleton** (i.e., global dictionary efficiently mapping
@@ -93,7 +93,7 @@ def __missing__(self, indent_level: int) -> str:
    '        '
 '''
 
-# ....................{ CODE ~ indent                      }....................
+# ....................{ STRINGS                            }....................
 CODE_INDENT_1 = INDENT_LEVEL_TO_CODE[1]
 '''
 Code snippet expanding to a single level of indentation.

beartype_test/a00_unit/a60_check/a00_code/snip/test_codesnipcls.py

@@ -0,0 +1,53 @@
+#!/usr/bin/env python3
+# --------------------( LICENSE                            )--------------------
+# Copyright (c) 2014-2024 Beartype authors.
+# See "LICENSE" for further details.
+
+'''
+Beartype **type-checking expression snippet class unit tests.**
+
+This submodule unit tests the public API of the public
+:mod:`beartype._check.code.snip.codesnipcls.PITH_INDEX_TO_VAR_NAME` submodule.
+'''
+
+# ....................{ IMPORTS                            }....................
+#!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
+# WARNING: To raise human-readable test errors, avoid importing from
+# package-specific submodules at module scope.
+#!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
+
+# ....................{ TESTS                              }....................
+def test_pith_index_to_var_name() -> None:
+    '''
+    Test the :obj:`beartype._check.code.snip.codesnipcls.PITH_INDEX_TO_VAR_NAME`
+    dictionary singleton.
+    '''
+
+    # ....................{ IMPORTS                        }....................
+    # Defer test-specific imports.
+    from beartype._check.code.snip.codesnipcls import PITH_INDEX_TO_VAR_NAME
+    from beartype._check.checkmagic import VAR_NAME_PITH_PREFIX
+    from pytest import raises
+
+    # ....................{ PASS                           }....................
+    # Assert this dictionary indexed by various positive integers creates and
+    # returns the expected local pith variable names.
+    assert PITH_INDEX_TO_VAR_NAME[1] == f'{VAR_NAME_PITH_PREFIX}1'
+    assert PITH_INDEX_TO_VAR_NAME[2] == f'{VAR_NAME_PITH_PREFIX}2'
+
+    # Assert this dictionary internally caches these constants.
+    assert PITH_INDEX_TO_VAR_NAME[1] is PITH_INDEX_TO_VAR_NAME[1]
+    assert PITH_INDEX_TO_VAR_NAME[2] is PITH_INDEX_TO_VAR_NAME[2]
+
+    # ....................{ FAIL                           }....................
+    # Assert that attempting to index this dictionary by non-integer indices
+    # raises the expected exception.
+    with raises(AssertionError):
+        PITH_INDEX_TO_VAR_NAME[2.34]
+
+    # Assert that attempting to index this dictionary by non-positive indices
+    # raises the expected exception.
+    with raises(AssertionError):
+        PITH_INDEX_TO_VAR_NAME[0]
+    with raises(AssertionError):
+        PITH_INDEX_TO_VAR_NAME[-1]