Add "no math constants" check

docs/categories.md

@@ -49,6 +49,11 @@ These checks cover:
 These checks relate to the [itertools](https://docs.python.org/3/library/itertools.html)
 standard library module.
 
+## `math`
+
+These checks relate to the [math](https://docs.python.org/3/library/math.html)
+standard library module.
+
 ## `operator`
 
 These checks relate to the [operator](https://docs.python.org/3/library/operator.html)

refurb/checks/math/use_constants.py

@@ -0,0 +1,56 @@
+from dataclasses import dataclass
+
+from mypy.nodes import FloatExpr
+
+from refurb.error import Error
+
+
+@dataclass
+class ErrorInfo(Error):
+    """
+    Don't hardcode math constants like pi, tau, or e, use the `math.pi`,
+    `math.tau`, or `math.e` constants respectively.
+
+    Bad:
+
+    ```
+    def area(r: float) -> float:
+        return 3.1415 * r * r
+    ```
+
+    Good:
+
+    ```
+    import math
+
+    def area(r: float) -> float:
+        return math.pi * r * r
+    ```
+    """
+
+    code = 152
+    categories = ["math", "readability"]
+
+
+CONSTANTS = {
+    "pi": "3.14",
+    "e": "2.71",
+    "tau": "6.28",
+}
+
+
+def check(node: FloatExpr, errors: list[Error]) -> None:
+    num = str(node.value)
+
+    if len(num) <= 3:
+        return None
+
+    for name, value in CONSTANTS.items():
+        if num.startswith(value):
+            errors.append(
+                ErrorInfo(
+                    node.line,
+                    node.column,
+                    f"Replace `{num}` with `math.{name}`",
+                )
+            )

test/data/err_123.py

@@ -4,7 +4,7 @@
 _ = bytes(b"hello world")
 _ = complex(1j)
 _ = dict({"a": 1})
-_ = float(3.14)
+_ = float(123.456)
 _ = list([1, 2, 3])
 _ = str("hello world")
 _ = tuple((1, 2, 3))
@@ -22,7 +22,7 @@
 d = {"a": 1}
 _ = dict(d)
 
-e = 3.14
+e = 123.456
 _ = float(e)
 
 f = [1, 2, 3]

test/data/err_152.py

@@ -0,0 +1,22 @@
+# these should match
+
+pi = 3.14
+pi = 3.1415
+pi = 003.1400
+pi = -3.14
+e = 2.71
+e = 2.71828
+e = -2.71
+tau = 6.28
+tau = 6.2831
+tau = 2 * 3.14
+tau = -6.28
+
+
+# these should not
+
+_ = 3.1
+_ = 2.7
+_ = 6.2
+_ = 1234
+_ = 3.0

test/data/err_152.txt

@@ -0,0 +1,11 @@
+test/data/err_152.py:3:6 [FURB152]: Replace `3.14` with `math.pi`
+test/data/err_152.py:4:6 [FURB152]: Replace `3.1415` with `math.pi`
+test/data/err_152.py:5:6 [FURB152]: Replace `3.14` with `math.pi`
+test/data/err_152.py:6:7 [FURB152]: Replace `3.14` with `math.pi`
+test/data/err_152.py:7:5 [FURB152]: Replace `2.71` with `math.e`
+test/data/err_152.py:8:5 [FURB152]: Replace `2.71828` with `math.e`
+test/data/err_152.py:9:6 [FURB152]: Replace `2.71` with `math.e`
+test/data/err_152.py:10:7 [FURB152]: Replace `6.28` with `math.tau`
+test/data/err_152.py:11:7 [FURB152]: Replace `6.2831` with `math.tau`
+test/data/err_152.py:12:11 [FURB152]: Replace `3.14` with `math.pi`
+test/data/err_152.py:13:8 [FURB152]: Replace `6.28` with `math.tau`