python - What does "table" in the string.translate function mean?

Question

Going through the string.translate function which says:

Delete all characters from s that are in deletechars (if present), and then translate the characters using table, which must be a 256-character string giving the translation for each character value, indexed by its ordinal. If table is None, then only the character deletion step is performed.

• What does table mean here? Can it be a dict containing the mapping?
• What does "must be a 256-character string" mean?
• Can the table be made manually or through a custom function instead of string.maketrans?

I tried using the function (attempts below) just to see how it worked but wasn't successfully able to use it.

>>> "abcabc".translate("abcabc",{ord("a"): "d", ord("c"): "x"})
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: translation table must be 256 characters long

>>> "abcabc".translate({ord("a"): ord("d"), ord("c"): ord("x")}, "b")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: expected a character buffer object

>>> "abc".translate({"a": "d", "c": "x"}, ["b"])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: expected a character buffer object

What am I missing here?

Answer 1

It depends on Python version you are using.

In Python 2.x. The table is 256-characters string. It can be created using string.maketrans:

>>> import string
>>> tbl = string.maketrans('ac', 'dx')
>>> "abcabc".translate(tbl)
'dbxdbx'

In Python 3.x, the table is mapping of unicode ordinals to unicode characters.

>>> "abcabc".translate({ord('a'): 'd', ord('c'): 'x'})
'dbxdbx'