import math
import cmath
print("calculo de las constantes generalizadas")
Z=input("ingrese el parametro Z ohm/km: ")
Y=input("ingrese el parametro Y siemen/km: ")
g=cmath.sqrt(Z*Y)
print(g)

Error:
Traceback (most recent call last):
  File "C:/Users/Usuario/AppData/Local/Programs/Python/Python37-32/test.py", line 6, in <module>
  g=cmath.sqrt(Z*Y)
TypeError: can't multiply sequence by non-int of type 'str'

https://docs.python.org/3/library/functions.html?highlight=complex#complex Wrote:class complex([real[, imag]])

• Return a complex number with the value real + imag*1j or convert a string or number to a complex number. If the first parameter is a string, it will be interpreted as a complex number and the function must be called without a second parameter. The second parameter can never be a string. Each argument may be any numeric type (including complex). If imag is omitted, it defaults to zero and the constructor serves as a numeric conversion like int and float. If both arguments are omitted, returns 0j.
  
  Note When converting from a string, the string must not contain whitespace around the central + or - operator. For example, complex('1+2j') is fine, but complex('1 + 2j') raises ValueError.
  The complex type is described in Numeric Types — int, float, complex.
  
  Changed in version 3.6: Grouping digits with underscores as in code literals is allowed
  

.