Apparently, the following is the valid syntax:
my_string = b'The string'
I would like to know:
b
character in front of the string mean?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 < 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?
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.
>>> len('Öl') # German word for 'oil' with 2 characters
2
>>> 'Öl'.encode('UTF-8') # convert str to bytes
b'\xc3\x96l'
>>> len('Öl'.encode('UTF-8')) # 3 bytes encode 2 characters !
3
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()
Here's an example where the absence of b
would throw a TypeError
exception in Python 3.x
>>> f=open("new", "wb")
>>> f.write("Hello Python!")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'str' does not support the buffer interface
Adding a b
prefix would fix the problem.
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
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'}
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:
str
as String
and bytes
as byte[]
;str
as NVARCHAR
and bytes
as BINARY
or BLOB
;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('>d', b'\xff\xf8\x00\x00\x00\x00\x00\x00')[0]
You can encode a str
to a bytes
object.
>>> '\uFEFF'.encode('UTF-8')
b'\xef\xbb\xbf'
And you can decode a bytes
into a str
.
>>> b'\xE2\x82\xAC'.decode('UTF-8')
'€'
But you can't freely mix the two types.
>>> b'\xEF\xBB\xBF' + 'Text with a UTF-8 BOM'
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
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.
>>> b'A' == b'\x41'
True
But I must emphasize, a character is not a byte.
>>> 'A' == b'A'
False
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
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 """..."""
allow multi-line string literals.
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.
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).
Source: Stackoverflow.com