INTRODUCTION – Managing Files with Python

PRACTICE QUIZ: MANAGING FILES & DIRECTORIES

1. The create_python_script function creates a new python script in the current working directory, adds the line of comments to it declared  by the ‘comments’ variable, and returns the size of the new file. Fill in the gaps to create a script called “program.py”.

def create_python_script(filename):
  comments = "# Start of a new Python program"
  with open(filename, 'w') as file:
    file.write(comments)
    filesize = file.tell()
  return filesize


print(create_python_script("program.py"))

2. The new_directory function creates a new directory inside the current working directory, then creates a new empty file inside the new directory, and returns the list of files in that directory. Fill in the gaps to create a file “script.py” in the directory “PythonPrograms”.

import os


def new_directory(directory, filename):
  # Before creating a new directory, check to see if it already exists
  if os.path.isdir(directory) == False:
    os.mkdir(directory)


  # Create the new file inside of the new directory
  os.chdir(directory)
  with open (filename, 'w') as file:
    pass


  # Return the list of files in the new directory
  return os.listdir()


print(new_directory("PythonPrograms", "script.py"))

3. Which of the following methods from the os module will create a new directory?

4. The file_date function creates a new file in the current working directory, checks the date that the file was modified, and returns just the date portion of the timestamp in the format of yyyy-mm-dd. Fill in the gaps to create a file called “newfile.txt” and check the date that it was modified.

import os
import datetime


def file_date(filename):
  # Create the file in the current directory
  with open(filename, 'w') as file:
    pass
  
  # Get the timestamp of when the file was last modified
  timestamp = os.path.getmtime(filename)


  # Convert the timestamp into a readable format, then into a string
  date_modified = datetime.datetime.fromtimestamp(timestamp).strftime('%Y-%m-%d')


  # Return just the date portion 
  # Hint: how many characters are in “yyyy-mm-dd”? 
  return ("{}".format(date_modified))


print(file_date("newfile.txt")) 
# Should be today's date in the format of yyyy-mm-dd

5. The parent_directory function returns the name of the directory that’s located just above the current working directory. Remember that ‘..’ is a relative path alias that means “go up to the parent directory”. Fill in the gaps to complete this function.

import os


def parent_directory():
  # Create a relative path to the parent 
  # of the current working directory 
  relative_parent = os.path.join(os.getcwd(), '..')


  # Return the absolute path of the parent directory
  return os.path.abspath(relative_parent)


print(parent_directory())

6. What is the difference between the readline() and read() methods?

7. Can you identify which code snippet will correctly open a file and print lines one by one without whitespace?

with open("hello_world.txt") as text:
    for line in text:
        print(line)

with open("hello_world.txt") as text:
    for line in text:
        print(text)

with open("hello_world.txt") as text:
    print(line)

with open("hello_world.txt") as text:
    for line in text:
        print(line.strip()) (CORRECT)

8. What happens to the previous contents of a file when we open it using “w” (“write” mode)?

9. How can we check if a file exists inside a Python script?

10. Some more functions of the os.path module include getsize() and isfile() which get information on the file size and determine if a file exists, respectively. In the following code snippet, what do you think will print if the file does not exist?

import os
file= "file.dat"
if os.path.isfile(file):
    print(os.path.isfile(file))
    print(os.path.getsize(file))
else:
    print(os.path.isfile(file))
    print("File not found")

file.dat
1024

False
2048

True
512

False
File not Found (CORRECT)

11. What’s the purpose of the os.path.join function?

PRACTICE QUIZ: READING & WRITING CSV FILES

1. We’re working with a list of flowers and some information about each one. The create_file function writes this information to a CSV file. The contents_of_file function reads this file into records and returns the information in a nicely formatted block. Fill in the gaps of the contents_of_file function to turn the data in the CSV file into a dictionary using DictReader.

import os
import csv


# Create a file with data in it
def create_file(filename):
  with open(filename, "w") as file:
    file.write("name,color,type\n")
    file.write("carnation,pink,annual\n")
    file.write("daffodil,yellow,perennial\n")
    file.write("iris,blue,perennial\n")
    file.write("poinsettia,red,perennial\n")
    file.write("sunflower,yellow,annual\n")


# Read the file contents and format the information about each row
def contents_of_file(filename):
  return_string = ""


  # Call the function to create the file 
  create_file(filename)


  # Open the file
  with open(filename, mode='r') as file:
    # Read the rows of the file into a dictionary
    reader = csv.DictReader(file)
    
    # Process each item of the dictionary
    for row in reader:
      return_string += "a {} {} is {}\n".format(row["color"], row["name"], row["type"])
  return return_string


# Call the function
print(contents_of_file("flowers.csv"))

2. Using the CSV file of flowers again, fill in the gaps of the contents_of_file function to process the data without turning it into a dictionary. How do you skip over the header record with the field names?

import os
import csv


# Create a file with data in it
def create_file(filename):
  with open(filename, "w") as file:
    file.write("name,color,type\n")
    file.write("carnation,pink,annual\n")
    file.write("daffodil,yellow,perennial\n")
    file.write("iris,blue,perennial\n")
    file.write("poinsettia,red,perennial\n")
    file.write("sunflower,yellow,annual\n")


# Read the file contents and format the information about each row
def contents_of_file(filename):
  return_string = ""


  # Call the function to create the file 
  create_file(filename)


  # Open the file
  with open(filename, mode='r') as file:
    # Read the rows of the file
    rows = csv.reader(file)
    
    # Process each row
    for row in rows:
      # Skip over the header record with field names
      if row[0] == "name":
          continue
      
      # Format the return string for data rows only
      return_string += "a {} {} is {}\n".format(row[1], row[0], row[2])
  return return_string


# Call the function
print(contents_of_file("flowers.csv"))

3. In order to use the writerows() function of DictWriter() to write a list of dictionaries to each line of a CSV file, what steps should we take? (Check all that apply)

4. Which of the following is true about unpacking values into variables when reading rows of a CSV file? (Check all that apply)

5. If we are analyzing a file’s contents to correctly structure its data, what action are we performing on the file?

6. If we have data in a format we understand, then we have what we need to parse the information from the file. What does parsing really mean?

7. Which of the following lines would correctly interpret a CSV file called “file” using the CSV module? Assume that the CSV module has already been imported.

8. Which of the following must we do before using the csv.writer() function?

9. DictReader() allows us to convert the data in a CSV file into a standard dictionary. DictWriter() \ allows us to write data from a dictionary into a CSV file. What’s one parameter we must pass in order for DictWriter() to write our dictionary to CSV format?

CONCLUSION – Managing Files with Python