CODEWITHSUNDEEP
pythonpython-3.xinput
Sela12
Sela12

Reputation: 65

Getting multible variables in Python in one line

I made this calculator using Python and I'm happy with it(considering it's my very first Python program). The only thing I would like to improve is the input system. This is my current way of getting the variables, but I have to enter each variable with a space between, like this: 2 + 3 * 4. What I would like to be able to do is to enter them without a space, like this: 2+3*4.

In C++ you can do:

std::cin >> num1 >> act1 >> num2 >> act2 >> num3;

My question is if there is a way to do the same thing in Python?

This is the code I'm using now to get the variables:

user_input=input("Enter a num1 act1 num2 act2 num3 (with a space between them): ")      #Gets the values
var1, action1, var2, action2, var3=user_input.split()           #assigns the values into the variables

Upvotes: 1

Views: 110

Answers (3)

moogle
moogle

Reputation: 110

You could look into the regular expression re module to parse the user input:

import re

user_input = input(...)

pattern = '(?P<num1>\d+)\s?(?P<act1>.)\s?(?P<num2>\d+)\s?(?P<act2>.)\s?(?P<num3>\d+)'
res = re.search(pattern, user_input)

your_first_number = res.group('num1')
your_first_action = res.group('act1')
# etc.
  • Each number (with 1 or more digits) is represented by (?P<num1>\d+), which is a re group I named num1.
  • The operator is represented in a similar fashion, where . is any single character, or an operator in this case.
  • There may be 0 or 1 spaces between each number and operator, which is represented by \s?.
  • And I repeat this pattern.

re makes it a little more complicated, but it's more flexible in terms how the user can type in his input.

Upvotes: 0

Roland Smith
Roland Smith

Reputation: 43543

The easiest way is to use eval, since this can calculate expressions for you.

However eval can be dangerous with untrusted input since by default it exposes the whole Python interpreter. This is not an issue for a program you use yourself, but could be problematic for say a module used in a web application.

In the example below (in IPython), I've tried to make it less dangerous by using the locals and globals options. The _locals dict is used to make some functions from the math module available for use in expressions. The _globals dict disables Python's built-ins. Also note that this is in Python 3 which uses floating point division for the / operator.

In [1]: import math

In [2]: _globals = {"__builtins__": None}

In [3]: _lnames = ('acos', 'asin', 'atan', 'ceil', 'cos', 'cosh', 'e', 'log', 'log10',
   ...:            'pi', 'sin', 'sinh', 'sqrt', 'tan', 'tanh')

In [4]: _locals = {k: eval('math.'+k) for k in _lnames}

In [5]: eval('2+3*4', _globals, _locals)
Out[5]: 14

In [6]: eval('1+2/3', _globals, _locals)
Out[6]: 1.667

In [7]: eval('sin(pi)', _globals, _locals)
Out[7]: 1.225e-16

In [8]: eval('cos(pi)', _globals, _locals)
Out[8]: -1

In [9]: eval('cos(pi/2)', _globals, _locals)
Out[9]: 6.123e-17

Note that the outputs of 7 and 9 (which should be 0) are caused by the limits on accuracy of floating point arithmatic.

Upvotes: 0

MalloyDelacroix
MalloyDelacroix

Reputation: 2293

You could do something like this:

user_input = '2+12*9'

numbers = ''.join([x if x.isnumeric() else ' ' for x in user_input])
operators = [x for x in user_input if not x.isnumeric()]

var1, var2, var3 = numbers.rsplit(' ')
action1, action2 = operators[0], operators[1]

Basically using list comprehension to separate out the numbers and then the operators, and then using rsplit to assign the numbers to their variables and assigning the operator variables by their index in the list. This method will also allow you to use numbers with multiple digits.

Upvotes: 1

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