Last Week if statement print statement input builtin function strings and methods for loop

This Week Practice with string methods and for loops Doctests Conversion specifiers New type list –methods –Nested lists –Looping through a list –Looping using range

Doctests Why do we use an example in our docstrings? –To show the user how to call our function –To ensure our function works properly We can test our function by using the doctest module.

Docstrings import doctest def count_spaces(s): ‘’’(str) -> int Return the number of spaces in s as an int. >>>count_spaces(‘’) 0 >>>count_spaces(‘ ‘) 1 >>>count_spaces(‘there are several spaces here.’) 4 ’’’

Doctests def count_spaces(s): count = 0 for char in s: if char == ‘ ‘: count += 1 return count if __name__ == ‘__main__’: doctest.testmod() # or for more details use doctest.testmod(verbose=True) What do these do? Let’s try it!

Visiting the Items in a String S Printing out the characters of the string English: for each char in S print the char Python: for char in S: print(char) Notes: char is a variable name for and in are Python key words

for loops Format: for variable in string: statements Example with strings: name = ”Edward” new = “” for letter in name: new = letter + new print(new)

Strings Using Conversion Specifiers We sometimes would like to insert values of variables into strings: A1 = 60 A2 = 75 A3 = 88 We would like: ‘The average of 60, 75 and 88 is ’ How do we print this with our variables? >>>print(‘The average of’, A1, ‘,’, A2, ‘ and ’, A3, ‘ is ’, (A1+A2+A3)/3) Does this work?

Strings Using Conversion Specifiers We displayed: ‘The average of 60, 75 and 88 is ’ Q. What’s wrong? A. Spacing is wrong around commas and periods. We have many more decimal places than wanted. Q. How can we fix it? A. Use conversion specifiers. >>>print(‘The average of %d, %d and %d is %.2f’ %(A1, A2, A3, (A1+A2+A3)/3.0)) The average of 60, 75 and 88 is

Common Conversion Specifiers %d display the object as a decimal integer %fdisplay the object as a floating point with 6 decimal places %.2fdisplay the object as a floating point with 2 decimal places %sdisplay the object as a string Q. What else do we use % for? A. Modulus. We say that % is overloaded.

Way to store many variables, e.g., students = [“Abby”, “Bob”, “Harry”, “Sara”, “Don”] grades_list = [85, 80, 82, 84, 83] misc = [“Kaya”, 2006, “July”, 20, True] students[0] = ? students[3] = ? grades_list[2] = ? grades_list[5] = ? Lists “Abby” “Sara” 82 error

Lists cont… grades_list = [85, 80, 82, 84, 83] grades_list[2] = 86 grades_list.append(90) grades_list == ?? Functions len(grades_list) outputs… max(grades_list) outputs… min(grades_list) outputs… sum(grades_list) outputs… [85, 80, 86, 84, 83, 90] work for strings too

students = [“Abby”, “Bob”, “Harris”, “Sara”, “Don”] students.sort() [“Abby”, “Bob”, “Don”, “Sara”, “Harris”] students.insert(2, “Charlie”) [“Abby”, “Bob”, “Charlie”, “Don”, “Sara”, “Harris”] students.append(“Kaya”) has the same result as students.insert( ????, “Kaya”) Lists -- Methods student.insert(len(students), “Kaya”)

student_grades = [[‘ ’, 72], [‘ ’, 90], [[‘ ’, 84]] student_grades[0] == student_grades[0][0] == student_grades[1][0] == student_grades[2][1] == Nested Lists -- Lists of Lists list [‘ ’,72] ‘ ’ ‘ ’ 84 ??

Slicing Lists or Strings Idea: Grab part of a list aka a slice of a list. countries = [‘Canada’, ‘France’, ‘China’, ‘Italy’, ‘India’] countries[0:2] == countries[3:] == countries[:4] == countries[s:t] means: start at index s include all list items up to but not including item t. [‘Canada’, ‘France’, ‘China’, ‘Italy’] ?? [‘Italy’, ‘India’]?? [‘Canada’, ‘France’] ??

Visiting the Items in a List L Printing out the list English: for each item in L print the item Python: for item in L: print(item)

For Loops -- Revisited Want to print the numbers from for num in [0, 1, 2, 3, 4, …, 99, 100]: print(num) Is there an easier way to do this? for num in range(0, 101): print(num) range(start, stop[,step]) returns a list of integers beginning with start to the last integer before stop. start can be omitted and defaults to 0 step can be omitted and defaults to 1

For Loops -- Revisited L1 = [1, 2, 3, 4] L2 = [‘A’, ‘B’, ‘C’, ‘D’] Want to print each element from L1 followed by the corresponding element from L2. for num in L1: print(num, ??) # How do we print the item from L2? Loop over indices: for index in range(len(L2)): print(L1[index], L2[index])