Question

Please create a python module named homework.py and implement the functions outlined below. Below you will find an explanation for each function you need to implement. When you are done please upload the file homework.py to Grader Than. Please get started as soon as possible on this assignment. This assignment has many problems, it may take you longer than normal to complete this assignment.

This assignment is supposed to test you on your understanding of reading and writing to a text file and working with JSON objects.

Hint: Work on the methods in the order they are found in the documentation below.

def read_last_line(file_path: str)->str:
    """
    Reads the last line of the file at the specified file path. The function returns the last line of the file as a
    string, if the file is empty it will return an empty string ("").
    :param file_path: A path to a file
    :return: The last line of the file
    """

def read(file_path: str)->str:
    """
    Reads the entire file at the specified file path. The function returns all the text in the file as a string, if
    the file is empty it will return an empty string ("").
    :param file_path: A path to a file
    :return: All the text in the file
    """

def write(file_path:str, text:str=''):
    """
    Clears the file at the specified file path then writes the specified line to the file. If the function is invoked
    without a line parameter or the line variable is None nothing is written to the file but the file should still be
    cleared. If the file does not exist a new file is created, regardless if a text is specified.
    :param file_path: A path to a file
    :param line: None
    :return:
    """

def write_last_line(file_path:str, text:str=''):
    """
    Writes the specified line to the file as the last line. If the text parameter does not start with a new line
    character this adds a new line character to the text parameter so that the text is written on the next line of
    the file. If the function is invoked without a line parameter or the line variable is None nothing is written to
    the file. If the file does not exist a new file is created, regardless if a text is specified.
    :param file_path: A path to a file
    :param text: The last line to be written to the file.
    :return: None
    """

def clear(file_path: str):
    """
    Clears the file at the specified file path.
    :param file_path: A path to a file
    :return: None
    """

def delete_last_line(file_path: str) -> str:
    """
    Removes the last line in the file at the specified file path. Then it saves the new value with the last line
    removed to the file. Finally it returns the deleted last line. If the file has nothing in it an empty
    string ("") is returned.
    :param file_path: A path to file
    :return: The text in the file with the last line removed
    """

def swap_value(file_path: str, key: str, replacement):
    """
    This function will be given a file path and a key. The file that the file path points to contains a json object.
    This function should, load the data in the file. Then replace the value associated with the key with replacement
    value. Then it should overwrite the current data in the file with the new changes. Finally it should return the
    old value.

    :param file_path: A path to file
    :param key: A key value in the JSON object saved in the file
    :param replacement: The new value that the key will be mapped to
    :return: The old value that the key used to be mapped to
    """

def update_transactions(file_path: str, transaction_list: list):
    """
    You are part of a team tasked to create an application that helps bankers by saving their transactions for them.
    Your job within the project is to implement the feature that actually saves the transactions to the hard drive.
    The scope of your task is that you will be given a file path to where the data should be written and a list of
    bank transaction objects to be written to the file. The file will contain a JSON array of transactions that the
    banker previously saved. The bankers at this bank are silly sometimes and they make duplicate transactions, your
    function should remove the duplicate transactions in the transaction_list and update the existing transaction list
    saved in the file with the new transactions. Make sure when you are preforming the update of the new transactions
    that you overwrite old transactions (transactions that already exist in the file) with duplicate new transactions
    (transactions that are found in the transaction_list). You will know that a transaction is a duplicate if it has
     the same ID.

    In the end the file should contain a JSON list with transaction Objects that have been updated with the new
    information from the transaction_list. The JSON list should contain no transactions with the same ID.

    The transaction object referred to here in is outlined below. In actual testing of your code the professors
    transaction object will be used, which will have all the documented functionality.

    class Transaction:

        def __init__(self, id:int, type:str, amount:float):
            self.id:int = id
            self.type:str = type
            self.amount:float = amount

        def __str__(self):
            return 'Transaction[%s] %s $%s' (self.id, self.type, self.amount)

        def __hash__(self):
            return hash(self.id)

        def __eq__(self, other):
            return hasattr(other,'id') and other.id == self.id

    :param file_path: A path to file blank file that holds a JSON list of existing transaction and where the new
     transaction data should be written
    :param transaction_list: A list of transaction
    :return: None
    """

I am new for this and I don't know how to create a file and all the things talked about here. I need help. thank you in advance

Answer 1

IN PYTHON WE CAN CREATE A FILE BY USING THE OPEN() METHOD WITH "w" ACCESS SPECIFIER :

IN FILES , ACCESS SPECIFIER SPECIFIES THE TYPE OF OPERATION (READ ,WRITE , APPEND ) THAT WE ARE GOING TO PERFORM ON THE FILE.

THE CODE BELOW CONTAINS ALL THE METHODS ASKED IN THE QUESTION :

# here notice the "r" access specifier to read the file
# readllines() method returns a list of all the lines in the file
#using the negative indexing , reading the last line 
def read_last_line(path):
    with open(path,"r") as f1:
        lines = f1.readlines()
        res = lines[-1]
        return res

# read() method returns all the content of a file in the form of string
def read_file(path):
    with open(path,"r") as f1:
        f1.read()
        f1.close()  

#here notice that "w" access specifier is used to write into a file
# All the contents will be erased and new content will be added
# Here "text" is written into file
 
def write_file(path,text):
    with open(path,"w") as f2:
        f2.write(text)
        f2.close()

# here notice that "a" access specifier is used to append content to a file
# appending means writing to the last line of the file 
def write_last_line(path,text):
    with open(path,"a") as f1:
        f1.write(text)
        f1.close()

# for clearing the content of the file , we use the truncate() method 
def clear(path):
    with open(path,"r") as f1:
        f1.truncate()
        f1.close()


def delete_last_line(path):
    with open(path,"r") as f1:
        d=f1.read()
        f1.close()
        m= d.split("\n")
        s= "\n".join(m[:-1])
        f1 = open("file.txt","w+")
        for i in range(len(s)):
            f1.write(s[i])
        f1.close()
def swap_values(path,key,replacment):
    with open(path , 'w') as f1:
        for line in inp:
            if line == key:
                out.write(line)
                continue
            else:
                out.write(prev)
                prev = line
    f1.close()

The update transactions method :

import json
def update_transactions(path,transactions):
    # Searching for a duplicate id value in the transactions list and removing it
    # Notice that we use a dictionary to  filter the duplicates because dictionary does not allow the 
    # duplicate values  
    unique = { each['id'] : each for each in transactions }.values()
    # dump() in json package is used to write the json list to a file
    # indent specifies the spacing that's required when writing json to the file
    with open(path, 'w', encoding='utf-8') as f1:
        json.dump(unique, f, ensure_ascii=False, indent=4)
    f1.close()

json package in python is used to perform operations relations to json objects.