Files

Exercise : Create Directory

Complete the functions given below, to behave as described by their docstrings, so that the code produces the given output.

import os

def create_dir(dir_name):
  """Create a directory dir_name in the current working directory
  
  Example:
  If the current directory is c:/foo/, create_dir('bar') creates 
  a c:/foo/bar directory.
  """
  pass # REPLACE WITH YOUR CODE HERE
  
  
def change_dir(relative_path):
  """Change to the directory dir_name relative to the current working directory
  
  Example:
  If the current directory is c:/foo/, change_dir('bar') changes 
  current working directory to c:/foo/bar
  """
  pass # REPLACE WITH YOUR CODE HERE
  
  
def print_current():
  """Print current working directory"""
  pass # REPLACE WITH YOUR CODE HERE 
  
  
def change_to_parent_dir():
  """Change to the parent directry of the current working directory
  
  Example:
  If the current directory is c:/foo/bar, change_to_parent_dir() changes 
  the working directory to c:/foo/
  """
  pass # REPLACE WITH YOUR CODE HERE
  
  
def check(dir_name):
  create_dir(dir_name)
  print_current()
  change_dir(dir_name)
  print_current()
  change_to_parent_dir()
  print_current()
  
check('foo')
check('bar')


    

    


    
    

output when run in repl.it

/home/runner
/home/runner/foo
/home/runner
/home/runner
/home/runner/bar
/home/runner

    

    


    
    

Exercise : File Stats

Complete the functions given below, to behave as described by their docstrings, so that the code produces the given output.

def get_file_content_as_list(filename):
  """Return content of the file as a list of lines
  
  The file is expected to be in the current working directory.
  The lines in the list contains trailing line breaks.
  
  Example:
  If the a.txt has two lines 'aaa' and 'bbb', 
  get_file_content_as_list('a.txt') returns ['aaa\n', 'bbb']
  """
  return [] # REPLACE WITH YOUR CODE


def get_file_stats(contents):
  """Given a list of lines, return line count and letter count as a dictionary
  
  Trailing line breaks (if any) are not counted for letter count.
  Spaces, even trailing spaces, are counted for letter count.
  Example:
  get_stats(['aaa\n', 'bbb']) returns {'lines': 2, 'letters': 6}
  """
  stats = []
  # ADD YOUR CODE HERE
  return stats


def analyze_file(filename):
  contents_as_list = get_file_content_as_list(filename)
  print('lines in file:', contents_as_list)
  stats = get_file_stats(contents_as_list)
  print('It has', stats[0], 'lines containing', stats[1], 'letters')

analyze_file('file1.txt')
analyze_file('file2.txt')

    

    


    
    

file1.txt (2 lines, 22 letters):

aaa bbb ccc
ddd eee fff

    

    


    
    

file2.txt (4 lines, 10 letters -- note: the last line has a trailing space, which adds up to 10 letters):

a
bb
ccc
ddd 

    

    


    
    

lines in file: ['aaa bbb ccc\n', 'ddd eee fff']
It has 2 lines containing 22 letters
lines in file: ['a\n', 'bb\n', 'ccc\n', 'ddd ']
It has 4 lines containing 10 letters

    

    


    
    

Exercise : Add Line Numbers

Complete the functions given below, to behave as described by their docstrings, so that the code produces the given output. Only one function needs to be modified.

def get_file_content_as_list(filename):
  """Return content of the file as a list of lines
  
  The file is expected to be in the current working directory.
  The lines in the list contains trailing line breaks.
  
  Example:
  If the a.txt has two lines 'aaa' and 'bbb', 
  get_file_content_as_list('a.txt') returns ['aaa\n', 'bbb']
  """
  f = open(filename, 'r')
  lines = f.readlines()
  f.close()
  return lines
  
def write_with_line_numbers(lines, filename):
  """Write the strings in lines to the file filename, after adding a line number to each line.
  
  Example:
  write_with_line_numbers(['aaa\n', 'bbb'], 'out.txt') writes the following content to out.txt
  1. aaa
  2. bbb
  """
  pass # REPLACE WITH YOUR CODE


def process_file(sourcefile, targetfile):
  """Copy the text in sourcefile to targetfile, but also add line numbers to each line.
  
  Example:
  Assume a.txt has the following text:
  aaa
  bbb
  process_file('a.txt', 'b.txt') results in b.txt having the following text:
  1. aaa
  2. bbb
  """
  contents = get_file_content_as_list(sourcefile)
  write_with_line_numbers(contents, targetfile)
  print(get_file_content_as_list(targetfile))
  
process_file('file1a.txt', 'file1b.txt')
process_file('file2a.txt', 'file2b.txt')


    

    


    
    

file1a.txt:

first line

second line
third line

    

    


    
    

file2a.txt:

hang in there

    

    


    
    

['1. first line\n', '2. \n', '3. second line\n', '4. third line']
['1. hang in there']

    

    


    
    

Exercise : Calculate GST

Suppose there is a CSV file in this format:

item,price
book,10.0
bag,50.0
"pens, pencils", 5.0

    

    


    
    

Write a program to calculate GST for each item at 7% and give the value as an additional column. The output should be in a new file.

item,price,GST
book,10.0,0.7
bag,50.0,3.5
"pens, pencils",5.0,0.35

    

    


    
    

Start with the following code:

import csv

def calculate_GST(source_file, target_file):
  """Read the data from the CSV file source_file and write 
  the data, including the calculated GST values, to the CSV file target_file
  """
  input_lines = read_csv_lines(source_file)
  updated_lines = []
  
  # ADD YOUR CODE HERE
  
  write_to_csv_file(updated_lines, target_file)
   
  
def read_csv_lines(filename):
  """Return the values in the csv file (specified by the filename) as a list of lists
  each list representing a row of the file.
  
  Example: If the file file1.csv has the following contents,
  item,price
  book,10.0
  read_csv_lines('file1.csv') returns [['item', 'price'], ['book', '10.0']]
  
  """
  return [] # REPLACE WITH YOUR CODE
  
  
def write_to_csv_file(lines, filename):
  """Write the given lines (a list of lists) to the CSV file (specified by filename)
  
  Example:
  write_to_csv_file([['item', 'price', 'GST'], ['book', '10.0', '0.7']], 'file2.txt')
  
  """
  pass # REPLACE WITH YOUR CODE
  

def process(source_file, target_file):
  
  calculate_GST(source_file, target_file)
  print(read_csv_lines(target_file))
  
  
process('itemlist1.csv', 'updated_itemlist1.csv')
process('itemlist2.csv', 'updated_itemlist2.csv')

    

    


    
    

itemlist2.csv:

item,price
bread,1.0
bananas,4.0

    

    


    
    

You can use the built-in function round to round floating point numbers to a specific number of decimal places. e.g.,

• round(1.98, 1) rounds 1.98 to one decimal place, giving you 2.0
• round(1.234, 2) gives 1.23 and round(1.2, 1) gives 1.2