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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def uni_char_code(a: str, b: str, c: str, d: str):
 """Convert unicode characters to integers. Converts four hexadecimal chars to the integer that the string represents. For example, uni_char_code('0','0','0','f') will return 15, and uni_char_code('0','0','f','f') returns 255. Returns a negative number on error, if a char was invalid. This is implemented by noting that char2hex() returns -1 on error, which means the result of ORing the char2hex() will also be negative. """

    return char2hex(a) << 12 | char2hex(b) << 8 | char2hex(c) << 4 | char2hex(d)