What does the b character do in front of a string literal

Question

Apparently  the following is the valid syntax   my string   b The string    I would like to know    What does this b character in front of the string mean  What are the effects of using it  What are appropriate situations to use it    I found a related question right here on SO  but that question is about PHP though  and it states the b is used to indicate the string is binary  as opposed to Unicode  which was needed for code to be compatible from version of PHP  lt  6  when migrating to PHP 6  I don t think this applies to Python   I did find this documentation on the Python site about using a u character in the same syntax to specify a string as Unicode  Unfortunately  it doesn t mention the b character anywhere in that document   Also  just out of curiosity  are there more symbols than the b and u that do other things

User · Answer

You can use JSON to convert it to dictionary

import json
data = b'{"key":"value"}'
print(json.loads(data))

{"key":"value"}

FLASK:

This is an example from flask. Run this on terminal line:

import requests
requests.post(url='http://localhost(example)/',json={'key':'value'})

In flask/routes.py

@app.route('/', methods=['POST'])
def api_script_add():
    print(request.data) # --> b'{"hi":"Hello"}'
    print(json.loads(request.data))
return json.loads(request.data)

{'key':'value'}

User · Answer

In addition to what others have said  note that a single character in unicode can consist of multiple bytes    The way unicode works is that it took the old ASCII format  7-bit code that looks like 0xxx xxxx  and added multi-bytes sequences where all bytes start with 1  1xxx xxxx  to represent characters beyond ASCII so that Unicode would be backwards-compatible with ASCII    gt  gt  gt  len    l      German word for  oil  with 2 characters 2  gt  gt  gt     l  encode  UTF-8      convert str to bytes  b  xc3 x96l   gt  gt  gt  len    l  encode  UTF-8       3 bytes encode 2 characters   3

User · Answer

To quote the Python 2 x documentation      A prefix of  b  or  B  is ignored in   Python 2  it indicates that the   literal should become a bytes literal   in Python 3  e g  when code is   automatically converted with 2to3   A    u  or  b  prefix may be followed by   an  r  prefix    The Python 3 documentation states      Bytes literals are always prefixed with  b  or  B   they produce an instance of the bytes type instead of the str type  They may only contain ASCII characters  bytes with a numeric value of 128 or greater must be expressed with escapes

User · Answer

From server side  if we send any response  it will be sent in the form of byte type  so it will appear in the client as b Response from server   In order get rid of b       simply use below code   Server file   stri  Response from server      c send stri encode      Client file   print s recv 1024  decode      then it will print Response from server

User · Answer

Python 3 x makes a clear distinction between the types   str         literals   a sequence of Unicode characters  Latin-1  UCS-2 or UCS-4  depending on the widest character in the string  bytes   b      literals   a sequence of octets  integers between 0 and 255   If you re familiar with   Java or C   think of str as String and bytes as byte    SQL  think of str as NVARCHAR and bytes as BINARY or BLOB  Windows registry  think of str as REG SZ and bytes as REG BINARY   If you re familiar with C      then forget everything you ve learned about char and strings  because a character is not a byte   That idea is long obsolete  You use str when you want to represent text  print               You use bytes when you want to represent low-level binary data like structs  NaN   struct unpack   gt d   b  xff xf8 x00 x00 x00 x00 x00 x00   0   You can encode a str to a bytes object   gt  gt  gt    uFEFF  encode  UTF-8   b  xef xbb xbf   And you can decode a bytes into a str   gt  gt  gt  b  xE2 x82 xAC  decode  UTF-8          But you can t freely mix the two types   gt  gt  gt  b  xEF xBB xBF     Text with a UTF-8 BOM  Traceback  most recent call last     File  quot  lt stdin gt  quot   line 1  in  lt module gt  TypeError  can t concat bytes to str  The b      notation is somewhat confusing in that it allows the bytes 0x01-0x7F to be specified with ASCII characters instead of hex numbers   gt  gt  gt  b A     b  x41  True  But I must emphasize  a character is not a byte   gt  gt  gt   A     b A  False  In Python 2 x Pre-3 0 versions of Python lacked this kind of distinction between text and binary data   Instead  there was   unicode   u      literals   sequence of Unicode characters   3 x str str         literals   sequences of confounded bytes characters  Usually text  encoded in some unspecified encoding  But also used to represent binary data like struct pack output     In order to ease the 2 x-to-3 x transition  the b      literal syntax was backported to Python 2 6  in order to allow distinguishing binary strings  which should be bytes in 3 x  from text strings  which should be str in 3 x    The b prefix does nothing in 2 x  but tells the 2to3 script not to convert it to a Unicode string in 3 x  So yes  b      literals in Python have the same purpose that they do in PHP   Also  just out of curiosity  are there more symbols than the b and u that do other things   The r prefix creates a raw string  e g   r  t  is a backslash   t instead of a tab   and triple quotes           or  quot  quot  quot     quot  quot  quot  allow multi-line string literals

User · Answer

Here s an example where the absence of b would throw a TypeError exception in Python 3 x   gt  gt  gt  f open  new    wb    gt  gt  gt  f write  Hello Python    Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  TypeError   str  does not support the buffer interface   Adding a b prefix would fix the problem

User · Answer

The answer to the question is that  it does  data encode    and in order to decode it remove the b  because sometimes you don t need it  use  data decode

User · Answer

The b denotes a byte string   Bytes are the actual data  Strings are an abstraction   If you had multi-character string object and you took a single character  it would be a string  and it might be more than 1 byte in size depending on encoding   If took 1 byte with a byte string  you d get a single 8-bit value from 0-255 and it might not represent a complete character if those characters due to encoding were   1 byte   TBH I d use strings unless I had some specific low level reason to use bytes

User · Answer

It turns it into a bytes literal  or str in 2 x   and is valid for 2 6    The r prefix causes backslashes to be  uninterpreted   not ignored  and the difference does matter

[python] What does the 'b' character do in front of a string literal?

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