pyrtan / src / pyrtan / conditions.py
4,740 bytes · last changed 2026-10-25 in Initial public release
| 1 | """Conditions for ``decide`` branches. |
| 2 | |
| 3 | A condition is a small table with one or more tests; all tests must hold. |
| 4 | Every test is a plain comparison a reader can check by eye, which is the |
| 5 | point: the branch taken is always explainable from the observed value and |
| 6 | the condition text. |
| 7 | |
| 8 | { eq = 200 } |
| 9 | { gte = 500 } |
| 10 | { matches = "^https://" } |
| 11 | { contains = "error" } |
| 12 | { in = ["open", "pending"] } |
| 13 | { exists = true } |
| 14 | { empty = false } |
| 15 | { between = [200, 299] } |
| 16 | { type = "list" } |
| 17 | """ |
| 18 | |
| 19 | from __future__ import annotations |
| 20 | |
| 21 | import re |
| 22 | from typing import Any |
| 23 | |
| 24 | from .template import MISSING |
| 25 | |
| 26 | KNOWN = {"eq", "ne", "lt", "lte", "gt", "gte", "matches", "contains", "in", "exists", "empty", "between", "type", "startswith", "endswith"} |
| 27 | |
| 28 | TYPE_NAMES = { |
| 29 | "str": str, |
| 30 | "string": str, |
| 31 | "int": int, |
| 32 | "float": float, |
| 33 | "number": (int, float), |
| 34 | "bool": bool, |
| 35 | "list": list, |
| 36 | "dict": dict, |
| 37 | "map": dict, |
| 38 | "null": type(None), |
| 39 | "none": type(None), |
| 40 | } |
| 41 | |
| 42 | |
| 43 | class ConditionError(ValueError): |
| 44 | pass |
| 45 | |
| 46 | |
| 47 | def validate(cond: Any) -> None: |
| 48 | if not isinstance(cond, dict) or not cond: |
| 49 | raise ConditionError("a condition is a non-empty table") |
| 50 | unknown = set(cond) - KNOWN |
| 51 | if unknown: |
| 52 | raise ConditionError(f"unknown condition keys: {sorted(unknown)}") |
| 53 | if "matches" in cond: |
| 54 | try: |
| 55 | re.compile(cond["matches"]) |
| 56 | except re.error as e: |
| 57 | raise ConditionError(f"bad regex in matches: {e}") from e |
| 58 | if "between" in cond and (not isinstance(cond["between"], list) or len(cond["between"]) != 2): |
| 59 | raise ConditionError("between takes a two-item list") |
| 60 | if "type" in cond and cond["type"] not in TYPE_NAMES: |
| 61 | raise ConditionError(f"unknown type {cond['type']!r}; one of {sorted(TYPE_NAMES)}") |
| 62 | if "in" in cond and not isinstance(cond["in"], list): |
| 63 | raise ConditionError("in takes a list") |
| 64 | |
| 65 | |
| 66 | def holds(cond: dict[str, Any], value: Any) -> bool: |
| 67 | """True when every test in ``cond`` holds for ``value``.""" |
| 68 | for key, expected in cond.items(): |
| 69 | if not _test(key, expected, value): |
| 70 | return False |
| 71 | return True |
| 72 | |
| 73 | |
| 74 | def _is_empty(value: Any) -> bool: |
| 75 | if value is MISSING or value is None: |
| 76 | return True |
| 77 | if isinstance(value, (str, list, dict, tuple)): |
| 78 | return len(value) == 0 |
| 79 | return False |
| 80 | |
| 81 | |
| 82 | def _num(value: Any) -> float | None: |
| 83 | if isinstance(value, bool): |
| 84 | return None |
| 85 | if isinstance(value, (int, float)): |
| 86 | return float(value) |
| 87 | if isinstance(value, str): |
| 88 | try: |
| 89 | return float(value.strip()) |
| 90 | except ValueError: |
| 91 | return None |
| 92 | return None |
| 93 | |
| 94 | |
| 95 | def _test(key: str, expected: Any, value: Any) -> bool: |
| 96 | if key == "exists": |
| 97 | return (value is not MISSING and value is not None) == bool(expected) |
| 98 | if key == "empty": |
| 99 | return _is_empty(value) == bool(expected) |
| 100 | if value is MISSING: |
| 101 | return False |
| 102 | if key == "eq": |
| 103 | return _loose_eq(value, expected) |
| 104 | if key == "ne": |
| 105 | return not _loose_eq(value, expected) |
| 106 | if key in ("lt", "lte", "gt", "gte"): |
| 107 | a, b = _num(value), _num(expected) |
| 108 | if a is None or b is None: |
| 109 | return False |
| 110 | return {"lt": a < b, "lte": a <= b, "gt": a > b, "gte": a >= b}[key] |
| 111 | if key == "between": |
| 112 | a, lo, hi = _num(value), _num(expected[0]), _num(expected[1]) |
| 113 | if a is None or lo is None or hi is None: |
| 114 | return False |
| 115 | return lo <= a <= hi |
| 116 | if key == "matches": |
| 117 | return value is not None and re.search(expected, str(value)) is not None |
| 118 | if key == "contains": |
| 119 | if isinstance(value, (list, tuple)): |
| 120 | return any(_loose_eq(item, expected) for item in value) |
| 121 | if isinstance(value, dict): |
| 122 | return expected in value |
| 123 | return str(expected) in str(value) |
| 124 | if key == "startswith": |
| 125 | return str(value).startswith(str(expected)) |
| 126 | if key == "endswith": |
| 127 | return str(value).endswith(str(expected)) |
| 128 | if key == "in": |
| 129 | return any(_loose_eq(value, option) for option in expected) |
| 130 | if key == "type": |
| 131 | return isinstance(value, TYPE_NAMES[expected]) and not (expected in ("int", "number", "float") and isinstance(value, bool)) |
| 132 | raise ConditionError(f"unknown condition key {key!r}") |
| 133 | |
| 134 | |
| 135 | def _loose_eq(a: Any, b: Any) -> bool: |
| 136 | """Equality that lets ``"200"`` match ``200`` but keeps bools strict.""" |
| 137 | if isinstance(a, bool) or isinstance(b, bool): |
| 138 | return a is b or (isinstance(a, bool) and isinstance(b, bool) and a == b) |
| 139 | if a == b: |
| 140 | return True |
| 141 | na, nb = _num(a), _num(b) |
| 142 | if na is not None and nb is not None and (isinstance(a, str) or isinstance(b, str)): |
| 143 | return na == nb |
| 144 | return False |