Creo que usas Python 3.
1.Opening a file in binary mode is simple but subtle. The only difference from opening it in text mode is that the mode parameter contains a 'b' character.
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4.Here’s one difference, though: a binary stream object has no encoding attribute. That makes sense, right? You’re reading (or writing) bytes, not strings, so there’s no conversion for Python to do.
http://www.diveintopython3.net/files.html#read
Luego, en Python 3, ya que un flujo binario a partir de un archivo es una secuencia de bytes, una expresión regular para analizar una corriente de un archivo deben ser definidas con una secuencia de bytes, no una secuencia charcaters.
In Python 2, a string was an array of bytes whose character encoding was tracked separately. If you wanted Python 2 to keep track of the character encoding, you had to use a Unicode string (u'') instead. But in Python 3, a string is always what Python 2 called a Unicode string — that is, an array of Unicode characters (of possibly varying byte lengths).
http://www.diveintopython3.net/case-study-porting-chardet-to-python-3.html
y
In Python 3, all strings are sequences of Unicode characters. There is no such thing as a Python string encoded in UTF-8, or a Python string encoded as CP-1252. “Is this string UTF-8?” is an invalid question. UTF-8 is a way of encoding characters as a sequence of bytes. If you want to take a string and turn it into a sequence of bytes in a particular character encoding, Python 3 can help you with that.
http://www.diveintopython3.net/strings.html#boring-stuff
y
4.6. Strings vs. Bytes# Bytes are bytes; characters are an abstraction. An immutable sequence of Unicode characters is called a string. An immutable sequence of numbers-between-0-and-255 is called a bytes object.
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1.To define a bytes object, use the b' ' “byte literal” syntax. Each byte within the byte literal can be an ASCII character or an encoded hexadecimal number from \x00 to \xff (0–255).
http://www.diveintopython3.net/strings.html#boring-stuff
Así que va a definir su expresión regular de la siguiente manera
pat = re.compile(b'[a-f]+\d+')
y no como
pat = re.compile('[a-f]+\d+')
Más explicaciones aquí:
15.6.4. Can’t use a string pattern on a bytes-like object
que supongo de la referencia a objeto bytes-como que está utilizando Python 3, ¿es correcto? –