challenge ：modules，error handling，list comprehensions

In this challenge, you'll practice using modules, classes, and list comprehensions to process and represent a data set in Python. You'll be working with data on NFL player suspensions.

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• Read the dataset into a list of lists.

  • Import the csv module.
  • Create a File handler for nfl_suspensions_data.csv.
  • Use the csv.reader() and list() methods to read the file into a list named nfl_suspensions.

• Remove the first list in nfl_suspensions, which contains the header row of the CSV file.

  • Select all lists in nfl_suspensions, except the for the one at index 0.
  • Assign the resulting list of lists back to the variablenfl_suspensions.

• Count the number of times each value in the year column occurs.

  • Create an empty dictionary called years.
  • Use a for loop to iterate over the list in nfl_suspensions representing theyear column:
    • Extract that row's value for the year column and assign it torow_year.
    • If row_year is already a key in years, add 1 to the value for that key.
    • If row_year isn't already a key in years, set the value for the key to 1.

• Use the print() function to display the dictionary years.

import csv

nfl_suspensions = list (csv.reader(open('nfl_suspensions_data.csv','r')))
nfl_suspensions = nfl_suspensions[1:]

years ={}
for row in nfl_suspensions:
    year = row[5]
    if year in years:
        years[year]+=1
    else:
        years[year] =1
print(years)

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Let's explore the values in these columns by using sets and list comprehensions.

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• Retrieve the unique values in the team column and assign the list to unique_teams.
  • Use a list comprehension to create a new list containined just the values in the team column.
  • Use the set() function to return a list containing only the unique values and assign to unique_teams.

• Retrieve the unique values in the games column and assign the list to unique_games.

  • Use a list comprehension to create a new list containined just the values in the games column.
  • Use the set() function to return a list containing only the unique values and assign to unique_games.

• Display unique_teams andunique_games.

teams = [row[1] for row in nfl_suspensions]
unique_teams = set(teams)

unique_games = set([row[2] for row in nfl_suspensions])

print (unique_teams)
print (unique_games)

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• Create the Suspension class.

  • Define the__init__() method with the following criteria:
    • The sole required parameter is a list representing a row from the dataset.
      • To create a Suspension instance, we want to be able to pass in a list from nfl_suspensions.
    • Currently, we're only interested in storing the name, team, games and year columns. Upon instantiation:
      • Set the name value for that row to the name property.
      • Set the team value for that row to theteam property.
      • Set the games value for that row to the gamesproperty.
      • Set the year value for that row to the year property.

• Create a Suspension instance using the third row in nfl_suspensions, and assign it to the variable third_suspension.

class Suspension:
    def __init__(self,row):
        self.name = row[0]
        self.team = row[1]
        self.games= row[2]
        self.year = row[3]
        
third_suspension = Suspension(nfl_suspensions[2])

print(third_suspension)
print(third_suspension.team)
print(third_suspension.name)

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Let's tweak the Suspension class a bit to extend its functionality. Right now, the value for year is a string, rather than an integer. Let's modify the Suspension class so that it stores the values as integers.

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• Instead of assigning the value at index 5 to the year property directly, use a try except block that:
  • Tries to cast the value at index 5 to an integer
  • If an exception is thrown, assign the value 0 to theyear property instead
• Create a method called get_year() that returns the year value for that Suspension instance.
• Create a Suspension instance using the 23rd row, and assign it to missing_year.
• Use the get_year() methodto assign the year of the missing_year suspension instance to twenty_third_year.

class Suspension:
    def __init__(self,row):
        self.name = row[0]
        self.team = row[1]
        self.games= row[2]
        try :
            self.year =int(row[5])
        except Exception:
            self.year = 0
    def get_year(self):
        return self.year
    
missing_year = Suspension(nfl_suspensions[22])
twenty_third_year = missing_year.get_year()
twenty_third_year

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