Making decimal.Decimal the default numerical type in Python

Question

Is there some way I could make decimal.Decimal the default type for all numerical values in Python? I would like to be able to use Python in a manner similar to the bc and dc programs without having to call decimal.Decimal(...) for every number.

EDIT: For the uninitiated: bc.

EDIT 2: Thank you tokenize module..

Are you talking about ensuring the python does floating point arithmetic instead of integer arithmetic? — seggy, Jan 18 '11 at 17:26
Perhaps you could hack the interpreter to do this, with a lot of effort. But why? When you write a Python program that needs decimal in some place, just use it there - way easier. If you need abritary precision decimals, use something that provides it. (And @seggy: float != decimal !!) — , Jan 18 '11 at 17:29
Yeah, I realized that after I posted. You're right, there doesn't seem to be a way that doesn't involve some serious mucking with python internals. Way more effort than the payoff would be worth, IMO. — seggy, Jan 18 '11 at 17:31
I will probably end up using the module that allows you to make your own interpreter. See [code module.](http://docs.python.org/library/code.html) — Eric Pruitt, Jan 18 '11 at 17:36
Where does the "numerical input" comes from in your program? It would probably be easier to force a conversion there rather than making your own interpreter... — unode, Jan 18 '11 at 17:40
The numerical input comes from me. I want to be able to use Python like bc and dc which are arbitrary precision calculators that support a scripting language. — Eric Pruitt, Jan 19 '11 at 00:10

Eric Pruitt · Accepted Answer · 2018-04-21T08:58:11.823

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At the bottom of the tokenize module's documentation, there is a function that does exactly what I need:

Python 3: "Example of a script rewriter that transforms float literals into Decimal objects"
Python 2: "Example of a script re-writer that transforms float literals into Decimal objects"

edited Apr 21 '18 at 08:58

answered Jan 19 '11 at 15:02

Eric Pruitt

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porgarmingduod · Answer 2 · 2011-01-20T15:33:36.363

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You cannot really do what you ask without some serious magic, which I won't try to touch upon in my answer, but there is at least a slightly easier way than doing decimal.Decimal(...)

from decimal import Decimal as D
num = D("1") + D("2.3")

Edit: use the shorter form from the comment.

edited Jan 20 '11 at 15:33

answered Jan 18 '11 at 17:29

porgarmingduod

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Well yes, I _could_ do it that way, but I was looking for something that didn't require explicit action for every number. – Eric Pruitt Jan 18 '11 at 17:32
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Also, It'd be more like `D("2.3")` so I don't lose precision. – Eric Pruitt Jan 18 '11 at 17:35
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The problem is that Python is a generic programming language, and is notable for not wanting magic stuff to happen. As the python saying goes: "Explicit is better than implicit." Which is why any answer you get to this question that does exactly what you want will be hackish. – porgarmingduod Jan 18 '11 at 17:40

Making decimal.Decimal the default numerical type in Python

2 Answers2