从Python的指数中提取数字

Question

Hi everyone / Python Gurus

I would like to know how to accomplish the following task, which so far I've been unable to do so.

Here's what I have:

Q1 = 20e-6

Now this is an exponential number that if you print(Q1) as is it will show: 2e-5 which is fine. Mathematically speaking.

However, here's what I want to do with it:

I want Q1 to print only the number 20. And based on the whether this is e-6 then print uC or if this e-9 the print nC.

Here's an example for better understanding:

Q1=20e-6

When I run print(Q1) show: 20uC.

Q2=20e-9

When I run print(Q2) show: 20nC.

Can you please help me figure this out?

Answer 1

just replace the exponent using str.replace:

q1 = 'XXXXXX'
q1 = q1.replace('e-9', 'nC').replace('e-6', 'uC')
print(q1)

Answer 2

You can try by splitting the string:

'20e-9'.split('e')

gives

['20', '-9']

From there on, you can insert whatever you want in between those values:

('u' if int(a[1]) > 0 else 'n').join(a)

(with a = '20e-9'.split('e') )

Answer 3

You can not. The behaviour you are looking for is called "monkey patching". And this is not allowed for int and float.

You can refer to this stackoverflow question

The only way I can think of is to create a class that extends float and then implement a __str__ method that shows as per your requirement.

------- More explanation -----

if you type

Q1 = 20e-6

in python shell and then

type(Q1) your will get a

float

So basically your Q1 is considered as float by python type system

when you type print(Q1) the _str__ method of float is called

The process of extending core class is one example of "monkey patch" and that is what I was refereing to.

Now the problem is that you can not "monkey patch" (or extend if you prefer that) core classes in python (which you can in some languages like in Ruby).

[int, float etc are core classes and written in C for your most common python distribution.]

So how do you solve it?

you need to create a new class like this

class Exponent(float): def init (self, value): self.value = value def __str__ (self): return "ok"

x = Exponent(10.0)
print(x) ==> "ok"

hope this helps

Answer 4

I recommend you using si-prefix .

You can install it using pip :

sudo pip install si-prefix

Then you can use something like this:

from si_prefix import si_format

# precision after the point
# char is the unity's char to be used
def get_format(a, char='C', precision=2):
    temp = si_format(a, precision)

    try:
        num, prefix = temp.split()
    except ValueError:
        num, prefix = temp , ''

    if '.' in num:
        aa, bb = num.split('.')
        if int(bb) == 0:
            num = aa

    if prefix:
        return num + ' ' + prefix + char
    else:
        return num


tests = [20e-6, 21.46e05, 33.32e-10, 0.5e03, 0.33e-2, 112.044e-6]
for k in tests:
    print get_format(k)

Output:

20 uC
2.15 MC
3.33 nC
500
3.30 mC
112.04 uC