### python

#### Lambda function asks for input twice,

I am working on a rather complicated math project using python but keep getting stuck with one problem:
a = lambda x: input('Function in terms of x')
This works until I have to run a command like:
z = a(n)
Every time this is done it asks for an input again so I get a console that looks like:
Function in terms of x:
Function in terms of x:
I know that I should theoretically be able to get around with the following:
func = input('Function: ')
a = lambda x: func
This creates another problem: x isn't defined in the outer scope, so I added sympy symbols like so:
x = sym.Symbol('x')
func = input('Function: ')
a = lambda x: func
but then running a command like this results in something weird:
Function: 5*x +1
>>>a(10)
5*x + 1
I think this is because lambda doesn't work with sympy, but I can't think of another way to get around the problem... Thank You for any help.
The full code is as follows; the function asks for the first input at line 18, and then at line 50 where it isn't supposed too. I believe that this has to do with the fact that I use the lambda function twice.
import matplotlib.pyplot as plt
import os
import time
from mpl_toolkits.mplot3d import axes3d
from sympy import *
import numpy as np
import tkinter as tk
from colorama import init, Fore, Back, Style
import mpmath
def main():
"""
Handling for Range and function
"""
rng = raw_input('Minimum, Maximum: ').split(',')
rng = [float(rng[i]) for i in range(2)]
a = lambda x: input('Function of x: ') # function a is the main polynomial#
"""
2 Dimensional Graph
"""
two_d_x = np.arange(rng[0], rng[1], abs(rng[1] - rng[0]) / 100)
two_d_y = a(two_d_x)
fig1 = plt.figure()
print [np.amin(two_d_x), np.amax(two_d_x), np.amin(two_d_y), np.amax(two_d_y)]
ax1.axis([np.amin(two_d_x), np.amax(two_d_x), np.amin(two_d_y), np.amax(two_d_y)])
ax1.plot(two_d_x, two_d_y, 'r-')
ax1.set_title(r'$\mathit{f(x)}\in \mathbb{R}^2$')
ax1.set_xlabel(r'$\mathit{x}$')
ax1.set_ylabel(r'$\mathit{y}$')
ax1.grid()
ax1.spines['left'].set_position('zero')
ax1.spines['right'].set_color('none')
ax1.spines['bottom'].set_position('zero')
ax1.spines['top'].set_color('none')
ax1.spines['left'].set_smart_bounds(True)
ax1.spines['bottom'].set_smart_bounds(True)
ax1.xaxis.set_ticks_position('bottom')
ax1.yaxis.set_ticks_position('left')
"""
Quiver Plot of Function
"""
u, v = np.meshgrid(np.arange(rng[0], rng[1], 1),
np.arange(rng[0], rng[1], 1))
### u+vj -> w+rjf
print False
output = a(u + (v * 1j))
print False
w = output.real
r = output.imag
ax2.axis([np.amin(w) * 1.1, np.amax(w) * 1.1, np.amin(r) * 1.1, np.amax(r) * 1.1])
distance = np.sqrt(((w - u) ** 2) + ((r - v) ** 2))
quiver_plot = ax2.quiver(u, v, w, r, distance, angles='xy', scale_units='xy', scale=1, cmap=plt.cm.jet)
plt.colorbar(quiver_plot, cmap=plt.cm.jet)
ax2.set_title(r'$\mathit{f(x)}\in \mathbb{C}^2$')
ax2.set_xlabel(r'$\mathit{rl}$')
ax2.set_ylabel(r'$\mathit{im}$')
ax2.grid()
ax2.spines['left'].set_position('zero')
ax2.spines['right'].set_color('none')
ax2.spines['bottom'].set_position('zero')
ax2.spines['top'].set_color('none')
ax2.spines['left'].set_smart_bounds(True)
ax2.spines['bottom'].set_smart_bounds(True)
ax2.xaxis.set_ticks_position('bottom')
ax2.yaxis.set_ticks_position('left')
plt.show()
main_program_loop = True
while main_program_loop == True:
print '| Quandri 1.0 | by: Boolean Designs\n'
main()
stay_loop_tp = True
while stay_loop_tp != False:
stay_loop_tp = raw_input("Would you like to continue using this program <yes/no>? ")
if stay_loop_tp == 'yes' or stay_loop_tp == 'y':
os.system('cls')
stay_loop_tp = False
elif stay_loop_tp == 'no' or stay_loop_tp == 'n':
print 'Exiting Quandri...'
time.sleep(1)
exit()
stay_loop_tp = False
else:
print "Improper Input."
time.sleep(2)
os.system('cls')

The sympy lib has support for parsing and evaluating expression:
import sympy
from sympy.parsing.sympy_parser import parse_expr
x = sympy.Symbol('x')
expression_string = input("Function: ")
expr = parse_expr(expression_string)
expr.evalf(subs={x:10})
see this http://docs.sympy.org/dev/modules/parsing.html
and this How to calculate expression using sympy in python
Edit: Thomas Kühn's answer is good, but in python2.7 raw_input must be used
f = raw_input("Function: ")
a = lambda x:eval(f)
print(a(10))

I don't know, if it is advisable to do something like this, but here is some code that works for me on python 3.5:
func = input('Function: ')
a = lambda x: eval(func)
print(a(10))
calling this script with python, I get:
Function: x+1
11

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