How to convert between bytes and strings in Python 3

Question

This is a Python 101 type question  but it had me baffled for a while when I tried to use a package that seemed to convert my string input into bytes    As you will see below I found the answer for myself  but I felt it was worth recording here because of the time it took me to unearth what was going on  It seems to be generic to Python 3  so I have not referred to the original package I was playing with  it does not seem to be an error  just that the particular package had a  tostring   method that was clearly not producing what I understood as a string      My test program goes like this   import mangler                                   spoof package  stringThing        lt Doc gt       lt Greeting gt Hello World lt  Greeting gt       lt Greeting gt    lt  Greeting gt   lt  Doc gt         print out the input print  This is the string input    print stringThing     now make the string into bytes bytesThing   mangler tostring stringThing       pseudo-code again    now print it out print   nThis is the bytes output    print bytesThing    The output from this code gives this   This is the string input    lt Doc gt       lt Greeting gt Hello World lt  Greeting gt       lt Greeting gt    lt  Greeting gt   lt  Doc gt    This is the bytes output  b  n lt Doc gt  n     lt Greeting gt Hello World lt  Greeting gt  n     lt Greeting gt  xe4 xbd xa0 xe5 xa5 xbd lt  Greeting gt  n lt  Doc gt  n    So  there is a need to be able to convert between bytes and strings  to avoid ending up with non-ascii characters being turned into gobbledegook

User · Answer

This is a Python 101 type question   It s a simple question but one where the answer is not so simple   In python3  a  quot bytes quot  object represents a sequence of bytes  a  quot string quot  object represents a sequence of unicode code points  To convert between from  quot bytes quot  to  quot string quot  and from  quot string quot  back to  quot bytes quot  you use the bytes decode and string encode functions  These functions take two parameters  an encoding and an error handling policy  Sadly there are an awful lot of cases where sequences of bytes are used to represent text  but it is not necessarily well-defined what encoding is being used  Take for example filenames on unix-like systems  as far as the kernel is concerned they are a sequence of bytes with a handful of special values  on most modern distros most filenames will be UTF-8 but there is no gaurantee that all filenames will be  If you want to write robust software then you need to think carefully about those parameters  You need to think carefully about what encoding the bytes are supposed to be in and how you will handle the case where they turn out not to be a valid sequence of bytes for the encoding you thought they should be in  Python defaults to UTF-8 and erroring out on any byte sequence that is not valid UTF-8   print bytesThing   Python uses  quot repr quot  as a fallback conversion to string  repr attempts to produce python code that will recreate the object  In the case of a bytes object this means among other things escaping bytes outside the printable ascii range

User · Answer

The  mangler  in the above code sample was doing the equivalent of this   bytesThing   stringThing encode encoding  UTF-8     There are other ways to write this  notably using bytes stringThing  encoding  UTF-8    but the above syntax makes it obvious what is going on  and also what to do to recover the string   newStringThing   bytesThing decode encoding  UTF-8     When we do this  the original string is recovered   Note  using str bytesThing  just transcribes all the gobbledegook without converting it back into Unicode  unless you specifically request UTF-8  viz   str bytesThing  encoding  UTF-8    No error is reported if the encoding is not specified

User · Answer

In python3  there is a bytes   method that is in the same format as encode     str1   b hello world  str2   bytes  hello world   encoding  UTF-8   print str1    str2    Returns True   I didn t read anything about this in the docs  but perhaps I wasn t looking in the right place  This way you can explicitly turn strings into byte streams and have it more readable than using encode and decode  and without having to prefex b in front of quotes

User · Answer

TRY THIS   StringVariable ByteVariable decode  UTF-8   ignore     TO TEST TYPE   print type StringVariable        Here  StringVariable  represented as a string   ByteVariable  represent as Byte  Its not relevent to question Variables

[string] How to convert between bytes and strings in Python 3?

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