What Do Backticks Mean to the Python Interpreter? Example: 'Num'

What do backticks mean to the Python interpreter? Example: `num`

Backticks are a deprecated alias for repr(). Don't use them any more; the syntax was removed in Python 3.0.

Using backticks seems to be faster than using repr(num) or num.__repr__() in version 2.x. I guess it's because additional dictionary lookup is required in the global namespace (for repr), or in the object's namespace (for __repr__), respectively.

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Using the dis module proves my assumption:

def f1(a):
    return repr(a)

def f2(a):
    return a.__repr__()

def f3(a):
    return `a`

Disassembling shows:

>>> import dis
>>> dis.dis(f1)
  3           0 LOAD_GLOBAL              0 (repr)
              3 LOAD_FAST                0 (a)
              6 CALL_FUNCTION            1
              9 RETURN_VALUE
>>> dis.dis(f2)
  6           0 LOAD_FAST                0 (a)
              3 LOAD_ATTR                0 (__repr__)
              6 CALL_FUNCTION            0
              9 RETURN_VALUE
>>> dis.dis(f3)
  9           0 LOAD_FAST                0 (a)
              3 UNARY_CONVERT
              4 RETURN_VALUE

f1 involves a global lookup for repr, f2 an attribute lookup for __repr__, whereas the backtick operator is implemented in a separate opcode. Since there is no overhead for dictionary lookup (LOAD_GLOBAL/LOAD_ATTR) nor for function calls (CALL_FUNCTION), backticks are faster.

I guess that the Python folks decided that having a separate low-level operation for repr() is not worth it, and having both repr() and backticks violates the principle

"There should be one-- and preferably only one --obvious way to do it"

so the feature was removed in Python 3.0.

Why does backtick string conversion work sporadically in my Django application?

Backticks are an alias for repr(), not for str(). There are types where repr() and str() return the same value, hence the confusion.

For user output, you should always use str(). Backticks probably shouldn't be used at all -- they have been removed in Python 3.x since they were considered a misfeature.

Use backticks (`) or double quotes () with Python and SQLite

The SQL standard says that strings must use 'single quotes', and identifiers (such as table and column names), when quoted, must use "double quotes".

For compatibility with MySQL, SQLite also allows to use single quotes for identifiers and double quotes for strings, but only when the context makes the meaning unambiguous. (In SELECT 'rowid' ..., a string is allowed, so a string is what you get.) If possible, always use the standard SQL quotes.

For compatibility with MySQL, SQLite also allows `backticks` for identifiers.

For compatibility with Microsoft databases, SQLite also allows [brackets] for identifiers.

(This works in all SQLite versions.)

Python: repr vs backquote

They're an alias for repr. They have the exact same effect.

However, they're deprecated and have been removed in Python 3. Don't use them; use repr.

Python strings and integer concatenation

NOTE:

The method used in this answer (backticks) is deprecated in later versions of Python 2, and removed in Python 3. Use the str() function instead.

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You can use:

string = 'string'
for i in range(11):
    string +=`i`
print string

It will print string012345678910.

To get string0, string1 ..... string10 you can use this as YOU suggested:

>>> string = "string"
>>> [string+`i` for i in range(11)]

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For Python 3

You can use:

string = 'string'
for i in range(11):
    string += str(i)
print string

It will print string012345678910.

To get string0, string1 ..... string10, you can use this as YOU suggested:

>>> string = "string"
>>> [string+str(i) for i in range(11)]

Python 2.x to 3.x - Append Syntaxerror: how to make it compatibale with Python 3.x from 2.x?

This is pretty neat historical syntax.

For backticks, I refer you to this answer: https://stackoverflow.com/a/1673087/2988730. The gist is that backticks are shorthand for calling repr until they were removed in python 3. They are mentioned in the docs as the "conversion" operation:

repr(object)

Return a string containing a printable representation of an object. This is the same value yielded by conversions (reverse quotes). It is sometimes useful to be able to access this operation as an ordinary function...

The append itself is a normal, though undocumented use of the ParsingError.append method:

def append(self, lineno, line):

Since version 3, ConfigParser had been renamed configparser, but still has the ParsingError.append method.

So you need a couple of changes:

1. At the beginning of the file, change from ConfigParser import ParsingError to

   from configparser import ParsingError

2. Change the line with the error to

   e.append(lineno, repr(line))
   

Note

The multiple arguments to append evoke, but aren't related to, a behavior of list.append that hasn't been supported since python 2.0. You can find a note here: https://docs.python.org/2/library/stdtypes.html#mutable-sequence-types. Specifically the footnote:

2. The C implementation of Python has historically accepted multiple parameters and implicitly joined them into a tuple; this no longer works in Python 2.0. Use of this misfeature has been deprecated since Python 1.4.

Perl backticks using bash

Capture::Tiny is a very nice option: as the SYNOPSIS shows, you can do

use Capture::Tiny 'capture';
my ($output, $error_output, $exit_code) = capture {
    system(@whatever);
};

as well as using system inside capture_stdout if you want the simpler behavior of backticks.

Plus it's very general-purpose, working on Perl code (even Perl code that does weird stuff) as well as external programs, so it's a good thing to have in your toolbox.

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