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

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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.

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.

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