Python for Bioinformatics

1. Python for Bioinformatics Midterm Solution

2. DO NOT PANIC CONDENSED ELEMENTARY MATERIAL TO BE COVERED IN CLASS AND AS OUTSIDE WORK REPLACEMENT EXAM (FOR bio STUDENTS) BUT NOT DURING REGULAR CLASS TIME

3. Problem 1 Write a Python program that prompts for and inputs two floating point values, then prints their sum and their average value. x = float(input("Enter first floating point number: ")) y = float(input("Enter second floating point number: ")) sum = x + y avg = sum/2 print("sum =",sum,", average =",avg) Always returns a string

4. Problem 2 Write a Python program that (a) prompts for and inputs as a single line the users first and last names (in that order) separated by a space (b) prints a line containing the user's last name, a comma, a space and the user's first name. Example (user input underlined): Enter your name (first, space, last): Jaydee AlexanderAlexander, Jaydee name = input("Enter your name (first, space, last): ") first,last = name.split() print(last,', ',first,sep='') L = name.split()L.reverse() print(', '.join(L))

5. Problem 3 Write a Python program that inputs a sentence and then prints the words of the sentence in reverse order. Words are separated by whitespace. Example (user input underlined): Enter a sentence: you can cage a swallow can't you you can't swallow a cage can you # input the sentence # split the sentence into a list of words # reverse the list of words # join the words back together separated by spaces # print the modified sentence

6. Problem 3 Write a Python program that inputs a sentence and then prints the words of the sentence in reverse order. Words are separated by whitespace. Example (user input underlined): Enter a sentence: you can cage a swallow can't you you can't swallow a cage can you sentence = input('Enter a sentence: ') words = sentence.split() words.reverse() s = ' '.join(words) print(s)

7. Problem 4 Write a Python functionwith one parameter, representing a test score, then returns the corresponding letter grade using the standard scale: greater than equal to 90 -> A, 80 to 89 -> B, 70 to 79 -> C, 60 to 69 -> D, less than 60 -> F. Your code must use the elif construct. def grade(score): if score >= 90: return 'A' elif score >= 80: return 'B' elif score >= 70: return 'C' elif score >= 60: return 'D' else: return 'F'

8. Problem 5 Write a python program that creates a dictionary whose keys are names (strings) and whose value for a key is a favorite food of the person with that name as follows: creates an empty dictionary; prompts for a name, prompts for a favorite food and then creates a corresponding entry in the dictionary. The program should keep inputting names and favorite foods until the user enters an empty string for the name. After creating the dictionary, the program prints one line per dictionary entry consisting of the name, the word "likes", and the value of the dictionary for that name. Example(user input underlined): Enter a sequence of names followed by a favorite food, terminating input by hitting enter for the name. Name: John Food: chocolate Name: Karen Food: dates Name: John likes chocolate Karen likes dates

9. Problem 5 Write a python program that creates a dictionary whose keys are names (strings) and whose value for a key is a favorite food of the person with that name as follows: creates an empty dictionary; prompts for a name, prompts for a favorite food and then creates a corresponding entry in the dictionary. The program should keep inputting names and favorite foods until the user enters an empty string for the name. After creating the dictionary, the program prints one line per dictionary entry consisting of the name, the word "likes", and the value of the dictionary for that name. # Create an empty dictionary # Input a name # while the name is not the empty string: # Input a food # Create a dictionary entry with key name and value food # Input a name # for key in D:# print key, "likes", dictionary value for key

10. Problem 5 Write a python program that creates a dictionary whose keys are names (strings) and whose value for a key is a favorite food of the person with that name as follows: creates an empty dictionary; prompts for a name, prompts for a favorite food and then creates a corresponding entry in the dictionary. The program should keep inputting names and favorite foods until the user enters an empty string for the name. After creating the dictionary, the program prints one line per dictionary entry consisting of the name, the word "likes", and the value of the dictionary for that name. # Create an empty dictionary D = {} name = input("Name: ") while(name != ''): food = input("Food: ") D[name] = food name = input("Name: ") for name in D: print(name,"likes",D[name]) # Guard against no names being entered # Dictionary entries created directly

11. Problem 6 Write a Python function half_backwards(L) with parameter a list L that returns the list consisting of the second half of L followed by the first half. Hint: a//b is the integer quotient obtained by dividing a by b. Examples : L = [1,2,3,4] K = half_backwards(L) # Now K == [3,4,1,2] defhalf_backwards(L): m = len(L)//2 + 1 first = L[:m] second = L[m:] return second+first L = [1,2,3,4,5] K = half_backwards(L) # Now K == [3,4,5,1,2] # L = [1,2,3,4,5] # m = 5//2 + 1 = 2 + 1 = 3 # first = L[:3] = [1,2] # second = L[3:] = [3,4,5] # second+first = [3,4,5,1,2]

12. Problem 7 Write a Python function that returns the number of lines of text in a file. defline_count(path): f = open(path,'r') L = f.readlines() f.close() return len(L) # open the file for reading # input the file's lines into a list # close the file # return the length of the list

13. Problem 8 Write a Python program that inputs an integer n and prints the sum of the fourth powers of the integers from 1 to n. n = int(input("Enter an integer: ")) sum = 0 for i in range(1,n+1): sum += i**4 print("The sum of the first",n, "positive integers is",sum)

14. Problem 9 Write a Python program that replaces every four-letter word in a text file with '****'. Assume words are separated by whitespace. # get the filename (path) from the user # open the file for reading # get the file contents as string S and# split into lines without '\n' # for each line:# split line into list of words # for each word in the line's word list # if word length is 4# replace the list entry with string of four asterisks # rebuild the line (join using separator ' ') # rebuild the file contents (join lines using separator '\n') # open file for writing and# write modified contents to file

15. Problem 9 Write a Python program that replaces every four-letter word in a text file with '****'. Assume words are separated by whitespace. fname = input("Enter an file name: ") with open(fname,'r') as f: # open file for reading S = f.read() # get contents as string S and L = S.splitlines() # split into lines without '\n' for i in range(len(L)): # for each line: K = L[i].split() # split line into list of words for j in len(K): # for each word of the line if len(K[j]) == 4: # if word length is 4 K[j] = '****' # replace with four asterisks L[i] = ' '.join(K) # rebuild the line S = '\n'.join(L) # rebuild the file contents with open(fname,'w') as f: # open file for writing andf.write(S)# write modified contents to file

16. Problem 9 Complete the code for the following Python function defOneToOne(D): """ returns True if no two keys of the dictionary D have the same value in the dictionary""" return len(D.values()) == len(D.keys()) Alternate Solution: defOneToOne(D): """ returns True if no two keys of the dictionary D have the same value in the dictionary""" return len(D.values()) == len(set(D.values()))