fix: pep8 refactor

Author: zhiyuajun

src/bad_style.py

@@ -1,86 +1,121 @@
-# NOTE: This file is intentionally written with poor style for the exam.
-# Your task: refactor to be PEP 8-friendly while keeping behavior unchanged.
+"""CLI tool for simple statistics (exam task).
 
-import math,os,sys
+This module is intentionally included in the exam with poor style in the
+starter version. The candidate should refactor it to be PEP 8 friendly
+without changing its observable behavior.
+"""
 
+from __future__ import annotations
 
-def calc(Arr,mode="mean",round_to=2, allow_negative=False):
-    """
-    do calculation for mean/median/std of list.
-    mode can be: mean,median,std.  round_to means rounding digits.
-    allow_negative False means raise if negative number in Arr
+import math
+import os
+import sys
+from collections.abc import Iterable
+
+
+def calc(
+    arr: Iterable[float] | None,
+    mode: str = "mean",
+    round_to: int = 2,
+    allow_negative: bool = False,
+) -> float | None:
+    """Calculate mean/median/std for a sequence.
+
+    Args:
+        arr: Input numbers. If None or empty, return None.
+        mode: One of "mean", "median", "std".
+        round_to: Number of decimal digits to round to.
+        allow_negative: If False, raise Exception when encountering negative value.
+
+    Returns:
+        Rounded statistic value, or None if arr is None/empty.
+
+    Raises:
+        Exception: When allow_negative is False and a negative value appears.
+        ValueError: When mode is unknown.
     """
-    if Arr==None or len(Arr)==0: return None
-    for x in Arr:
-        if (not allow_negative) and x<0:
-            raise Exception("negative not allowed: "+str(x))
-
-    if mode=="mean":
-        s=0
-        for x in Arr: s+=x
-        v=s/len(Arr)
-    elif mode=="median":
-        B=sorted(Arr)
-        n=len(B)
-        mid=n//2
-        if n%2==1: v=B[mid]
-        else: v=(B[mid-1]+B[mid])/2
-    elif mode=="std":
-        m=calc(Arr,"mean",round_to,allow_negative)
-        s=0
-        for x in Arr:
-            s+=(x-m)**2
-        v=math.sqrt(s/len(Arr))
+    if arr is None:
+        return None
+
+    values = list(arr)
+    if not values:
+        return None
+
+    if not allow_negative:
+        for x in values:
+            if x < 0:
+                # Keep behavior compatible with the original tests.
+                raise Exception(f"negative not allowed: {x}")
+
+    if mode == "mean":
+        value = sum(values) / len(values)
+    elif mode == "median":
+        sorted_values = sorted(values)
+        n = len(sorted_values)
+        mid = n // 2
+        if n % 2 == 1:
+            value = sorted_values[mid]
+        else:
+            value = (sorted_values[mid - 1] + sorted_values[mid]) / 2
+    elif mode == "std":
+        mean_value = calc(values, "mean", round_to, allow_negative)
+        assert mean_value is not None
+        value = math.sqrt(sum((x - mean_value) ** 2 for x in values) / len(values))
     else:
-        raise ValueError("Unknown mode:"+mode)
+        raise ValueError(f"Unknown mode:{mode}")
 
-    return round(v,round_to)
+    return round(value, round_to)
 
 
-def parse_numbers(text):
-    # expects "1,2,3" or "1 2 3" but does it badly
-    if text is None: return []
-    t=text.replace(","," ").replace("\t"," ")
-    parts=t.split(" ")
-    out=[]
-    for p in parts:
-        if p.strip()=="":
-            continue
-        out.append(float(p))
-    return out
+def parse_numbers(text: str | None) -> list[float]:
+    """Parse numbers from a string.
+
+    Accept input like:
+    - "1,2,3"
+    - "1 2 3"
+    - "1\\t2\\t3"
+    """
+    if text is None:
+        return []
+
+    normalized = text.replace(",", " ").replace("\t", " ")
+    return [float(p) for p in normalized.split()]
 
 
-def read_file(path):
-    # reads first line
-    f=open(path,"r")
-    line=f.readline()
-    f.close()
-    return line
+def read_file(path: str) -> str:
+    """Read the first line from the file."""
+    with open(path, encoding="utf-8") as f:
+        return f.readline()
 
 
-def main(argv=None):
-    if argv is None: argv=sys.argv
-    if len(argv)<3:
+def main(argv: list[str] | None = None) -> int:
+    """Entry point for CLI.
+
+    Usage:
+        python -m src.bad_style <mode> <numbers_or_file_path> [--file]
+    """
+    if argv is None:
+        argv = sys.argv
+
+    if len(argv) < 3:
         print("Usage: python -m src.bad_style <mode> <numbers_or_file_path> [--file]")
         return 2
 
-    mode=argv[1]
-    value=argv[2]
-    is_file=False
-    if len(argv)>3 and argv[3]=="--file":
-        is_file=True
+    mode = argv[1]
+    value = argv[2]
+    is_file = len(argv) > 3 and argv[3] == "--file"
 
     if is_file:
         if not os.path.exists(value):
-            print("file not found:"+value)
+            print(f"file not found:{value}")
             return 2
-        value=read_file(value)
+        value = read_file(value)
 
-    nums=parse_numbers(value)
-    r=calc(nums,mode=mode)
-    print(r)
+    nums = parse_numbers(value)
+    result = calc(nums, mode=mode)
+    print(result)
     return 0
 
 
-if __name__=="__main__":
-    raise SystemExit(main())
+if __name__ == "__main__":
+    raise SystemExit(main())