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 File Handling

Scenario

Prof. Jekyll conducts classes with students and regularly makes notes in a text file. Each line of the file contains three elements: the student's first name, the student's last name, and the number of point the student received during certain classes.

The elements are separated with white spaces. Each student may appear more than once inside Prof. Jekyll's file.

The file may look as follows:

John Smith 5 Anna Boleyn 4.5 John Smith 2 Anna Boleyn 11 Andrew Cox 1.5

samplefile.txt

Your task is to write a program which:

  • asks the user for Prof. Jekyll's file name;
  • reads the file contents and counts the sum of the received points for each student;
  • prints a simple (but sorted) report, just like this one:
Andrew Cox 1.5 Anna Boleyn 15.5 John Smith 7.0

output

Note:

  • your program must be fully protected against all possible failures: the file's non-existence, the file's emptiness, or any input data failures; encountering any data error should cause immediate program termination, and the erroneous should be presented to the user;
  • implement and use your own exceptions hierarchy - we've presented it in the editor; the second exception should be raised when a bad line is detect, and the third when the source file exists but is empty.

Tip: Use a dictionary to store the students' data.

Cisco:

# A base exception class for our code:

class StudentsDataException(Exception):

    pass



# An exception for erroneous lines:

class BadLine(StudentsDataException):

    def __init__(self, line_number, line_string):

        super().__init__(self)

        self.line_number = line_number

        self.line_string = line_string



# An exception for an empty file.

class FileEmpty(StudentsDataException):

    def __init__(self):

        super().__init__(self)



from os import strerror


# A dictionary for students' data:

data = { }


file_name = input("Enter student's data filename: ")

line_number = 1

try:

    f = open(file_name, "rt")

    # Read the whole file into list.

    lines = f.readlines()

    f.close()

    # Is the file empty?

    if len(lines) == 0:

        raise FileEmpty()

    # Scan the file line by line.

    for i in range(len(lines)):

        # Get the i'th line.

        line = lines[i]

        # Divide it into columns.

        columns = line.split()

        # There shoule be 3 columns - are they there?

        if len(columns) != 3:

            raise BadLine(i + 1, line)

        # Build a key from student's given name and surname.

        student = columns[0] + ' ' + columns[1]

        # Get points.

        try:

            points = float(columns[2])

        except ValueError:

            raise BadLine(i + 1, line)

        # Update dictionary.

        try:

            data[student] += points

        except KeyError:

            data[student] = points

    # Print results.

    for student in sorted(data.keys()):

        print(student,'\t', data[student])


except IOError as e:

    print("I/O error occurred: ", strerror(e.errno))

except BadLine as e:

    print("Bad line #" + str(e.line_number) + " in source file:" + e.line_string)

except FileEmpty:

    print("Source file empty")


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