My code is not accepting strings, and it is checking the wrong variable

So I am trying to make a function, plot, that will take f as a function ( I used cos in my shell), a and b as ranges with b greater than a.(B = 1 and A = 0 default), with n intervals, and m as the method of Riemann sum(center, left, or right.)

But the problem is that when I run the code and try to tye in right as a method, it does the following.

import numpy as np
import matplotlib.pyplot as plt

def plot(f, a = 0, b = 1, m = str('center'), n = 10):


    v = 0
    par = (b - a)/1000
    x = np.arange(a, b, par)
    plt.plot(x, f(x), 'black')
    w = (b - a)/n

##This is juts plotting the graph, does not need to be grouped

    if b < a:
        raise ValueError('Value b must be greater than a', b)

##Check if b is greater than a

    if m != str('center') or m != str('left') or m != str('right'):
        raise ValueError('Value m must be one of the following: center, left, or right', b)

##Check if  m is valid

    if n < 0:
        raise ValueError('N must be a positive integer', n)

##Check if n is positive and an integer

    if m == 'center':
        d = w /2
        x2 = np.arange(a + d , b + d , w)
        plt.bar(x2,f(x2), align = 'center', color = 'blue',\
                edgecolor = 'black', width = w, alpha = 0.5)
        print("The estimation using", m ,"is", v)
        plt.show()

##Does Mid Point

    if m == 'left':
        x2 = np.arange(a , b , w)
        plt.bar(x2,f(x2), align = 'edge', color = 'red',\
                edgecolor = 'black', width = w, alpha = 0.5)
        print("The estimation using", m ,"is", v)
        plt.show()

##Does Left Point

    if m == 'right':
        x2 = np.arange(a + w, b + w , w)
        plt.bar(x2,f(x2), align = 'edge', color = 'orange',\
                edgecolor = 'black', width = -w, alpha = 0.5)
        print("The estimation using", m ,"is", v)
        plt.show()


##Does Right Point

Traceback (most recent call last):
  File "<pyshell#44>", line 1, in <module>
    p2.plot(f)
  File "C:\Users\Vincent\AppData\Local\Programs\Python\Python37-32\Project2.py", line 21, in plot
    raise ValueError('Value m must be one of the following: center, left, or right', b)
ValueError: ('Value m must be one of the following: center, left, or right', 1)

This is the error message that I get. I didn't type in 1 for m, I typed in 1 for b but it is reading it somehow.