Plotting normal distribution curves with python

#-*-coding:utf-8-*-
"""
Plotting standard normal distribution curves in python
"""
# ==============================================================
import numpy as np
import math
import  as plt


def gd(x, mu=0, sigma=1):
  """Calculate the value of the dependent variable from the independent variable x according to the equation

  Argument.
    x: array
      Input data (independent variable)
    mu: float
      Mean value
    sigma: float
      Variance
  """
  left = 1 / ((2 * ) * (sigma))
  right = (-(x - mu)**2 / (2 * sigma))
  return left * right


if __name__ == '__main__':
  # Independent variables
  x = (-4, 5, 0.1)
  # Dependent variable (different means or variances)
  y_1 = gd(x, 0, 0.2)
  y_2 = gd(x, 0, 1.0)
  y_3 = gd(x, 0, 5.0)
  y_4 = gd(x, -2, 0.5)

  # Mapping
  (x, y_1, color='green')
  (x, y_2, color='blue')
  (x, y_3, color='yellow')
  (x, y_4, color='red')
  # Setting up the coordinate system
  (-5.0, 5.0)
  (-0.2, 1)

  ax = ()
  ['right'].set_color('none')
  ['top'].set_color('none')
  .set_ticks_position('bottom')
  ['bottom'].set_position(('data', 0))
  .set_ticks_position('left')
  ['left'].set_position(('data', 0))

  (labels=['$\mu = 0, \sigma^2=0.2$', '$\mu = 0, \sigma^2=1.0$', '$\mu = 0, \sigma^2=5.0$', '$\mu = -2, \sigma^2=0.5$'])
  ()