How to distinquish between floats, ints and scientific notation

Question

I’m writing a custom json compresser. It is going to be reading numbers in all formats. How do I print the values of the json in the format, it is given, with json.load(). I would also want to preserve the type.

Example of a file it would have to read would be:

{"a":301, "b":301.0, "c":3.01E2, "d":"301", "e":"301.0", "f":"3.01E2"}

I would also want it to be able to distinquish between 1, 1.0 and true

When I do a basic for loop to print the values and their types with json.load(), it prints out

301 int
301.0 float
301.0 float
301 str
301.0 str
3.01E2 str

And yes, I understand that scientific notations are floats

Excpected output would be

301 int
301.0 float
3.01E2 float
301 str
301.0 str
3.01E2 str

Asked By: user15555955

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Source

Answer 1

So IIUC you want to keep the formatting of the json even if the value is given as float. I think the only way to do this is to change the type in your json i.e. adding quotes around float elements.

This can be done with regex:

import json
import re

data = """{"a":301, "b":301.0, "c":3.01E2, "d":"301", "e":"301.0", "f":"3.01E2", "g": true, "h":"hello"}"""

# the cricial part: enclosing float/int in quotes:
pattern = re.compile(r'(?<=:)s*([+-]?d+(?:.d*(?:E-?d+)?)?)b')
data_str = pattern.sub(r'"1"', data)

val_dict = json.loads(data) # the values as normally read by the json module
type_dict = {k: type(v) for k,v in val_dict.items()} # their types
repr_dict = json.loads(data_str) # the representations (everything is a sting there)

# using Pandas for pretty formatting
import pandas as pd
df = pd.DataFrame([val_dict, type_dict, repr_dict], index=["Value", "Type", "Repr."]).T

Output:

    Value             Type   Repr.
a     301    <class 'int'>     301
b   301.0  <class 'float'>   301.0
c   301.0  <class 'float'>  3.01E2
d     301    <class 'str'>     301
e   301.0    <class 'str'>   301.0
f  3.01E2    <class 'str'>  3.01E2
g    True   <class 'bool'>    True
h   hello    <class 'str'>   hello

So here the details of the regex:

([+-]?d+(?:.d*(?:E-?d+)?)?) this is our matching group, consisting of:
- [+-]? optional leading + or –
- d+ one or more digits, followed by (optionally):
- (?:.d*(?:E-?d+)?)?: non capturing group made of
  - . a dot
  - d* zero or more digits
  - (optionally) an E with an (optional) minus - followed by one or more digits d+
b specifie a word boundary (so that the match doesn’t cut a series of digits)
(?<=:) is a lookbehind, ensuring the expression is directly preceeded by : (we don’t add quotes around existing strings)
s* any white character before the expression is ignored/removed

1 is a back reference to our (1st) group. So we replace the whole match with "1"

Edit: slightly changed the regex to replace numbers directly following : and taking leading +/- into account

Answered By: Tranbi

How to distinquish between floats, ints and scientific notation

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