python thousands separator formatting with different character without using locale-CodePudding

I am looking to format thousands with an apostrophe (but could be something else) without using locale or a replace method.

The comma that is used by default in the string formatting must be defined somewhere in the Python source code but I can't find where. Is it possible to access it and change it once so that all formatting in the same session uses the new character?

To be clear (edit after @Matiss comment), I do not want to change the formatting syntax. It should stay as f"{value:,}". However, instead of inserting commas, I would like to insert something else.

Hopefully the comma is declared as a constant somewhere in Python source code (for example string._THOUSANDS_SEPARATOR), and just re-assigning it to soemthing else will do the trick.

I can not find that constant definition.

For example, one of the ways to do it now is:

>>> val = 123456
>>> print(f"{val:,}".replace(",", "'"))
123'456

The replace method is cumbersome and has to be repeated every time. I also want to avoid the locale environment.

If the comma , is defined as a constant somewhere in Python source code, say for example in a module called python_formatting_constants, and the name of the constant was for example THOUSANDS_SEPARATOR, one could do:

>>> from python_formatting_constants import THOUSANDS_SEPARATOR
>>> THOUSANDS_SEPARATOR = "'"
>>> print(f"{val:,}") # the "," in the formatting string stays the same
123'456
>>> # but the formatted string uses the apostrophe instead of the comma

CodePudding user response：

If you want to do the changes from the core of python, then you might need help from python language developers. But You can create your own format specs by creating your own class and override any provided format specs does not work for you.

class MyInt(int):
    def __new__(cls, number):
        return super(MyInt, cls).__new__(cls, number)

    def __init__(self, value):
        self.value = value

    def __format__(self, format_spec):
        if format_spec == ",":
            return format(self.value, ",").replace(",", "'")
        return format(self.value, format_spec)

Here I have created my own class which is a subclass of int and I have overloaded the __format__ built-in method of int according to your need.

Example:

# Input
test_value = TestClass(1000)
"{:,}".format(test_value) # alternative: f"{test_value:,}"
# Output
"1'000"

It is just a dummy example, You can do more deep dive into format_spec argument of __format__ method to have your own and replace any existing identifier with your own.

My suggestion will be, it will be quite easier to create your own format_spec than waiting to get some help from core python development team.

Few caveats:

If you are planning to do some add, subtract ... etc with integer and your new class, then you also have to overload all those functions for example __add__, __sub__ because any numeric operation will return pure int but not MyInt which has its own formatting.

Example:

# input
another_value = test_value   2500
"{:,}".format(another_value)
# output
'3,500'

As you can see, the return value of is a int but not MyInt so it has used , in the output instead. So you have to do all numeric operation beforehand and then wrap the final numeric result with the MyInt for just to have proper formatting.

More details about the format specs here.