Python中reverseBits函数报错ValueError及行号异常问题排查

Let’s break down the two issues you’re facing and how to resolve them:

1. The ValueError: Unknown format code 'b' for object of type 'str' #

This error occurs because you’re passing a string to the reverseBits method instead of an integer. The format specifier 'b' is meant to convert integers to their binary string representation—when you pass a string (like "123" instead of 123), Python can’t apply the 'b' code to it, hence the error.

To fix this:

• Ensure you call the method with an integer argument (e.g., obj.reverseBits(10) instead of obj.reverseBits("10")).
• If you need to handle string inputs, add a conversion check at the start of the method:

  def reverseBits(self, n):
      if isinstance(n, str):
          n = int(n)
      # Rest of your code...
  

2. The Mysterious Line 20 Error #

The line number in the traceback refers to the line in your full source file, not just the snippet you shared. Since your reverseBits method is part of a class (evidenced by the self parameter), the actual line where '{0:08b}'.format(n) is written is line 20 in your entire file—even though it’s only the second line in your snippet. That’s why the line number seems mismatched.

3. Fixing the Return Value Issue #

Even if you resolve the input type error, your current code returns a reversed iterator object, which isn’t a usable result for reversing bits. You need to convert that iterator back to a string, then to an integer. Here’s the corrected full method:

def reverseBits(self, n):
    # Ensure input is an integer
    if not isinstance(n, int):
        raise TypeError("Input must be an integer (or convertible to one)")
    
    # Convert n to an 8-bit binary string (padded with leading zeros)
    binary = '{0:08b}'.format(n)
    
    # Reverse the binary string (join the reversed iterator into a string)
    reversed_binary = ''.join(reversed(binary))
    
    # Convert the reversed binary string back to an integer
    return int(reversed_binary, 2)

Example Usage: #

# For n = 10 (binary: 00001010)
obj.reverseBits(10)  # Returns 80 (binary: 01010000)

内容的提问来源于stack exchange，提问作者Daniel Paczuski Bak