CODEWITHSUNDEEP
pythonuser-inputdefault-valuestring-conversionmultiple-input
Plums
Plums

Reputation: 25

Multiple User-inputs, Default input, and String-to-Array Conversion

Hello all I would like to make a program that takes in two user inputs. The first is a scalar and the second is a provided list or array. The number would be a multiplier for which to scale the array and the output would be the multiplied array.

import numpy as np

a = [1, 3, 5, 7, 9]
b = [2, 4, 6, 8, 10]

Also, for added convenience to the user, I'd like there to be a default scalar of 1 if no number is entered.

I am sorry for the lack of code but everything I've tried has not worked anyway.

I know that using

x, y = input().split()

will enable the user to enter two inputs such as

3 a

or 

5.5 b

which is how I'd like the inputs to be entered. However, while the number can be converted to a float, I do not know how to interpret the letter a or b from a string to the their array names.

float(x)*np.array(y)

The following error I believe to have occurred due to the mismatch of data types.

 float(x)*np.array(y)
TypeError: ufunc 'multiply' did not contain a loop with signature matching types dtype('<U32') dtype('<U32') dtype('<U32')

If anyone can offer a solution or if there is a better way to do this than your input would be greatly appreciated. Thank you.

Upvotes: 0

Views: 241

Answers (2)

Som Shekhar Mukherjee
Som Shekhar Mukherjee

Reputation: 8188

I guess this helps! This also handles the case where the user doesn't specify a multiplier, then it automatically defaults to 1

import numpy as np

a = np.array([1, 3, 5, 7, 9])
b = np.array([2, 4, 6, 8, 10])

y,*x = input().split()
if not x:
    x=[1]

print(float(x[0])*eval(y))

Upvotes: 2

Reupiey
Reupiey

Reputation: 277

There are two solutions for your issue, one is cleaner.

The first one (dirty) consists in using eval, because the a or b your user will pass as input will be evaluated as a string, not as your variable named a. So you have to return float(x) * eval(y).

But the use of eval is heavily discouraged.

I think a cleaner way is to declare your pre-defined arrays in a dict and to look for the key the user provided like that:

import numpy as np

arrays = {
    "a": np.array([1, 3, 5, 7, 9]),
    "b": np.array([2, 4, 6, 8, 10])
}

coefficient, array_name = input().split()

print(float(coefficient) * arrays[array_name])

NB: In your original code, a = [1, 3, 5, 7, 9] defines a list. And you cannot multiply a float and a list. You could eventually multiply and int and a list but that is not what you want, it will duplicate your list :)

Upvotes: 1

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