Import type hint syntax from the future.

Also remove `_ensure_spacing`, no longer used.

src/nested_pandas/nestedframe/utils.py

@@ -1,44 +1,10 @@
+# typing.Self and "|" union syntax don't exist in Python 3.9
+from __future__ import annotations
+
 import ast
 from enum import Enum
 
 
-def _ensure_spacing(expr) -> str:
-    """Ensure that an eval string has spacing"""
-    single_val_operators = {"+", "-", "*", "/", "%", ">", "<", "|", "&", "~", "="}  # omit "(" and ")"
-    check_for_doubles = {"=", "/", "*", ">", "<"}
-    double_val_operators = {"==", "//", "**", ">=", "<="}
-    expr_list = expr
-
-    i = 0
-    spaced_expr = ""
-    while i < len(expr_list):
-        if expr_list[i] not in single_val_operators:
-            spaced_expr += expr_list[i]
-        else:
-            if expr_list[i] in check_for_doubles:
-                if "".join(expr_list[i : i + 2]) in double_val_operators:
-                    if spaced_expr[-1] != " ":
-                        spaced_expr += " "
-                    spaced_expr += expr_list[i : i + 2]
-                    if expr_list[i + 2] != " ":
-                        spaced_expr += " "
-                    i += 1  # skip ahead an extra time
-                else:
-                    if spaced_expr[-1] != " ":
-                        spaced_expr += " "
-                    spaced_expr += expr_list[i]
-                    if expr_list[i + 1] != " ":
-                        spaced_expr += " "
-            else:
-                if spaced_expr[-1] != " ":
-                    spaced_expr += " "
-                spaced_expr += expr_list[i]
-                if expr_list[i + 1] != " ":
-                    spaced_expr += " "
-        i += 1
-    return spaced_expr
-
-
 class NestingType(Enum):
     """Types of sub-expressions possible in a NestedFrame string expression."""