Python中EBCDIC(CP037)编码转大型机时部分值异常求助

我用Python实现EBCDIC(CP037)编码并向大型机发送文件，多数场景运行正常，但部分值转换结果异常。例如：

• 十六进制值43被转为BC、56被转为DA；
• 输入340312时结果正确，但输入343012时得到错误的3BC012。

以下是相关转换函数：

COMP-3转换函数 #

def unsigned_comp3(decimal_num, bytecount):
    sign_nibble = "1111"  # F for positive numbers
    # Convert the decimal number to a string of BCD digits
    bcd_str = ''.join([f"{int(d):04b}" for d in str(decimal_num)])
    bcd_len = len(bcd_str)
    # Add a leading nibble of "1111" to indicate that the number is packed in COMP-3 format
    bcd_str = bcd_str + sign_nibble
    print(f'bcd{decimal_num}: {bcd_str}')
    # Group the BCD digits into pairs of bytes
    byte_pairs = [bcd_str[i:i + 8] for i in range(0, len(bcd_str),8)]
    print(f'bytes{decimal_num}: {byte_pairs}')
    # Convert each byte pair to its hexadecimal equivalent
    hex_str = ''.join([f"{int(pair, 2):02X}" for pair in byte_pairs])
    # To EBCDIC
    output_str = to_ebcdic(hex_str, len(str(decimal_num)), bytecount)
    # Return hex string
    return output_str

EBCDIC转换函数 #

def to_ebcdic(input_str, input_length, bytecount):
    # Store the last character
    sign_char = input_str[-1]
    # Concatenate the remaining character and the sign character
    if sign_char == "D":
        # Remove the first character
        stripped_str = input_str[1:]
        input_hex = stripped_str[:input_length - 1] + sign_char
    elif sign_char == "F":
        input_hex = input_str[:input_length] + sign_char
    else:
        # Remove the first character
        stripped_str = input_str[1:]
        input_hex = stripped_str[:input_length] + sign_char
    # Padding if input_str is less than bytecount
    pad_str = pad_string(input_hex, bytecount)
    print(f'{pad_str}')
    # Convert the hex string to bytes
    input_bytes = bytearray.fromhex(pad_str)
    print(f'input bytes{input_str}: {input_bytes}')
    # Decode the bytes using EBCDIC encoding
    ebcdic_str = input_bytes.decode('cp037')
    print(f'ebcdic string{input_str}: {ebcdic_str}')
    # Return the decoded string
    return ebcdic_str

异常示例 #

大型机侧显示输入343012F时转换结果错误。

内容的提问来源于stack exchange，提问作者amandeep gandhi