command from terminal input and output will save an assigning directory - python-3.x

Question

In command line, I want to give python hist.py -n 1000 -o /dir and output will be png in the assigning directory. Can anyone help on it?
import numpy as np
import matplotlib.mlab as mlab
import matplotlib.pyplot as plt
import argparse
import os, sys, errno
def plotData(outputDir):
outFilename = "hist.pdf"
outFilepath = os.path.join(outputDir)
parser = argparse.ArgumentParser()
parser.add_argument("-n","--number", help="display a square of a given number",type=int)
parser.add_argument('-o', '--outputDir', required=True,
help='The directory to which plot files should be saved')
args = parser.parse_args()
num=(args.number)
outFilepath=(args.outputDir)
# example data
mu = 100 # mean of distribution
sigma = 15 # standard deviation of distribution
#num=input()
x = mu + sigma * np.random.randn(int(num))
num_bins = 50
# the histogram of the data
n, bins, patches = plt.hist(x, num_bins, normed=1, facecolor='green', alpha=0.5)
# add a 'best fit' line
y = mlab.normpdf(bins, mu, sigma)
plt.plot(bins, y, 'r--')
plt.xlabel('Smarts')
plt.ylabel('Probability')
plt.title(r'Histogram of IQ: $\mu=100$, $\sigma=15$')
# Tweak spacing to prevent clipping of ylabel
plt.subplots_adjust(left=0.15)
plt.savefig (outFilepath,outFilename)
plt.show()
plt.close()
I could give random variable but not directory from terminal command line.
I have used args.outputDir but it does not work for me.
and i am learners