Day19

Day 19: File Input/Output

Instructions:

1. Open a new python file.
2. Before working with files, make sure to import the os package and change the directory to the desired location if required. In Python Enhancement Proposal (PEP) 20 an Easter Egg was added to python. By executing import this, the "Zen of Python" by Tim Peters is provided. This is a collection of aphorisms that succinctly describe the guiding principles of Python's design, according to Guido van Rossum (the Benevolent Dictator for Life).

   import this
   import os
   
   print(os.getcwd())
   os.chdir('./Module2/Day19')
   

3. First we need to decrypt the "Zen of Python."

   zen = ""
   for letter in list(this.s):
       if letter in list(this.d.keys()):
           zen += this.d[letter]
       else:
           zen += letter
   print(zen)
   

4. By using the built-in open() function, a file can be created in the current working directory (cwd) to save the "Zen of Python" for future use. The open(filename, mode) function requires the first argument to contain the name of the file and the second argument is either w for write, r for read, and a for append. Once a file is no longer needed, the .close() method is required.

   with open('zen.txt', 'w') as z:
       z.write(zen)
   z.close()
   

5. With the r option, an existing file can be read. Similar to the w option, the .close() method must be used after the file is no longer required. Additionally, the .readline() method produces the entire line of the file or a specific number of characters specified within the parentheses. For each instance of .readline(), a subsequent line in the file will be provided.

   with open('declaration.txt', 'r') as d:
       print(d.readline())
       print(d.readline(25))
   d.close()
   

6. By using a for loop, all lines in the file can be written in a single operation. Using the end='' option, the default newline character is not used to eliminate adding a duplicate newline character.

   with open('farewell.txt', 'r') as d:
       for lines in d:
           print(lines, end='')
   d.close()
   

7. The append status can be used to add additional content to an existing file. Once the file to be appended is open, the file to append can be opened in read status. The file= option within the print statement allows the content to printed to the open file. Since a file with an active append status cannot be read. The file must be closed and reopened in read status to confirm the action was successful.

   # Read the file in the original state.
   print("{:=^50}\n".format(" BEFORE APPEND "))
   with open('constitution.txt', 'r') as c:
       for lines in c:
           print(lines, end='')
   c.close()
   
   # Appending action
   with open('constitution.txt', 'a') as c:
       print('\n', file=c)
       with open('billofrights.txt', 'r') as b:
           for lines in b:
               print(lines, end='', file=c)
       b.close()
   c.close()
   
   # Confirmation of successful appending.
   print("\n\n{:=^50}\n".format(" AFTER APPEND "))
   with open('constitution.txt', 'r') as c:
       for lines in c:
           print(lines, end='')
   c.close()
   

8. The rename() function can be used to update the name of a file.
   os.rename('constitution.txt', 'constitutionBillOfRights.txt')
9. Update the log file with what you have learned today.