Python Course homework 2

2018年10月31日，老文章

Exercise 1

Part 1: Given two numeric lists or tuples x_vals and y_vals of equal length, compute their inner product using zip()

Part 2: In one line, count the number of even numbers in 0,…,99

• Hint: x % 2 returns 0 if x is even, 1 otherwise

Part 3: Given pairs = ((2, 5), (4, 2), (9, 8), (12, 10)), count the number of pairs (a, b) such that both a and b are even

# -*- coding: utf-8 -*-
"""
Created on Tue Oct 30 17:15:44 2018

@author: Wengsway

"""

# Part 1
x_vals , y_vals = (1,2,3),(4,5,6)
sum = 0
for x,y in zip(x_vals,y_vals):
      sum = sum + x*y
print("The inner product is:", sum)

# Part 2
print(len([n for n in range(0,100) if n%2==0]))

# Part 3
pairs = ((2,5),(4,2),(9,8),(12,10))
count = 0
for i in pairs:
      if i[0]%2 == 0 and i[1]%2 == 0:
            count = count + 1
print(count)

Exercise 2

Consider the polynomial

Write a function p such that p(x, coeff) that computes the value in (1) given a point x and a list of coefficients coeff

Try to use enumerate() in your loop

# -*- coding: utf-8 -*-
"""
Created on Tue Oct 30 18:41:28 2018

@author: Wengsway

"""

def p(x,coeff):
      sum = 0
      for index,coeffvalue in enumerate(coeff):
            sum = sum + coeffvalue * (x**index)
      return sum
print(p(2,[1,2,3]))

Exercise 3

Write a function that takes a string as an argument and returns the number of capital letters in the string

Hint: 'foo'.upper() returns 'FOO'

略

Exercise 4

Write a function that takes two sequences seq_a and seq_b as arguments and returns True if every element in seq_a is also an element of seq_b, else False

• By “sequence” we mean a list, a tuple or a string
• Do the exercise without using sets and set methods

# -*- coding: utf-8 -*-
"""
Created on Tue Oct 30 22:50:43 2018

@author: Wengsway

"""

def sequence(seq_a,seq_b):
      counts = 0
      for i in range(len(seq_a)):
            if seq_a[i] in seq_b:
                  counts = counts + 1
      if counts == len(seq_a):
            return True
      else:
            return False
print(sequence([1,2,3,4,5],[1,2,3,4,5,6]))

Exercise 5

When we cover the numerical libraries, we will see they include many alternatives for interpolation and function approximation

Nevertheless, let’s write our own function approximation routine as an exercise

In particular, without using any imports, write a function linapprox that takes as arguments

• A function f mapping some interval [a,b][a,b] into ℝR
• two scalars a and b providing the limits of this interval
• An integer n determining the number of grid points
• A number x satisfying a <= x <= b

and returns the piecewise linear interpolation of f at x, based on n evenly spaced grid points a = point[0] < point[1] < ... < point[n-1] = b

Aim for clarity, not efficiency

# -*- coding: utf-8 -*-
"""
Created on Tue Oct 30 22:57:41 2018

@author: Wengsway

"""

def linapprox(a,b,n,x):
      f = lambda x: 1/(x**2+1)
      point = [a]
      for i in range(1,n):
            point.append(point[0]+(i*(b-a))/(n-1))
      for j in range(n-1):
            if x>=point[j] and x<point[j+1]:
                  y = f(point[j])*(1-(x-point[j])/(point[j+1]-point[j]))+f(point[j+1])*(x-point[j])/(point[j+1]-point[j])
      return y
fit = round(linapprox(0,1,11,0.55),4)
print(fit)