Question

python programming:

Can you please add comments to describe in detail what the following code does:

import os,sys,time

sl = []
try:
   f = open("shopping2.txt","r")
   for line in f:
       sl.append(line.strip())
   f.close()
except:
   pass

def mainScreen():
   os.system('cls') # for linux 'clear'
   print("%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%")
   print(" SHOPPING LIST ")
   print("%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%")
   print("\n\nYour list contains",len(sl),"items.\n")
   print("Please choose from the following options:\n")
   print("(a)dd to the list")
   print("(d)elete from the list")
   print("(v)iew the list")
   print("(q)uit the program")
   choice = input("\nchoice: ")
   if len(choice) > 0:
       if choice.lower()[0] == "a":
           addScreen()
       elif choice.lower()[0] == "d":
           deleteScreen()
       elif choice.lower()[0] == "v":
           viewScreen()
       elif choice.lower()[0] == "q":
           sys.exit()
       else:
           mainScreen()
   else:
       mainScreen()

def addScreen():
   global sl
   os.system('cls') # for linux 'clear'
   print("%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%")
   print(" ADD SCREEN ")
   print("%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%")
   print("\n\n")
   print("Please enter the name of the item that you want to add.")
   print("Press ENTER to return to the main menu.\n")
   item = input("\nItem: ")
   if len(item) > 0:
       sl.append(item)
       print("Item added :-)")
       saveList()
       time.sleep(1)
       addScreen()
   else:
       mainScreen()

def viewScreen():
   os.system('cls') # for linux 'clear'
   print("%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%")
   print(" VIEW SCREEN ")
   print("%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%")
   print("\n\n")
   for item in sl:
       print(item)

   print("\n\n")
   print("Press enter to return to the main menu")
   input()
   mainScreen()

def deleteScreen():
   global sl
   os.system('cls') # for linux 'clear'
   print("%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%")
   print(" DELETE SCREEN ")
   print("%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%")
   count = 0
   for item in sl:
       print(count, " - ", item)
       count = count + 1
   print("What number to delete?")
   choice = input("number: ")
   if len(choice) > 0:
       try:
           del sl[int(choice)]
           print("Item deleted...")
           saveList()
           time.sleep(1)
       except:
           print("Invalid number")
           time.sleep(1)
       deleteScreen()

   else:
       mainScreen()

def saveList():
       f = open("shopping2.txt", "w")
       for item in sl:
           f.write(item+"\n")
       f.close()

mainScreen()

Answer 1

Hi, In this program first It calls the function mainScreen, In the mainScreen it shows the menu . Here menu has infinate loop.

# importing required libraby files
import os,sys,time

#we declared s1 this is an array type of string to store the data from the file shopping2.txt file
sl = []

# try is an type of exception handling. If suppose in our program shopping2.txt file not available in our system then
# the program will terminate suddenly with some exception which is called abnormal termination.

#if we are use try it will handle the exception. In our program if file not found then it will goto except: and just pass / skip the code.
# you can print like "File ot found" for the knowing the programmer about to fie.

#Here we open a file by using predefined function in python i.e open in this we passed,
#file name and the mode of file. r means read mode. Just we retriving the data from the text file
try:
f = open("shopping2.txt","r")

# line is an local veriable and we get each string from the file (f)
for line in f:
       #we append / add the string int to the s1 string array.
       # strip method is used to remove any empty spaces before the string as well as end of the string.
sl.append(line.strip())
     
   #we should close the file. If we didn't close the file which is already open, might be get exception.
f.close()
except:
pass

#this function / definition called and display the menu .
def mainScreen():
  
   #here cls means clear the screen of console.
os.system('cls') # for linux 'clear'
print("%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%")
print(" SHOPPING LIST ")
print("%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%")
print("\n\nYour list contains",len(sl),"items.\n")
print("Please choose from the following options:\n")
print("(a)dd to the list")
print("(d)elete from the list")
print("(v)iew the list")
print("(q)uit the program")

#here we getting the input from the console. we sholud give like a,d,v and q based on the menu.
choice = input("\nchoice: ")

#It checks the length of entered input and it should be > zero
if len(choice) > 0:
       #if condition is true then it invokes corresponding function.
       # lower method converts if the user enter A then it converts A to 'a'. if user enter 'a' then a to 'a' no issu.
if choice.lower()[0] == "a":
addScreen()
elif choice.lower()[0] == "d":
deleteScreen()
elif choice.lower()[0] == "v":
viewScreen()
elif choice.lower()[0] == "q":
sys.exit()   #if user enter q then it will exit from the entaire prorgram.
else:
mainScreen()   #if user entered another key which is not in our menu. then again it invokes the main function.
else:
mainScreen()    # if conidition is not true it invokes main function. until we press q it will execute continuously.

def addScreen():
   #goabl s1 means we can access s1 from any where in this program and we can use as well as.
global sl
os.system('cls') # for linux 'clear'
print("%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%")
print(" ADD SCREEN ")
print("%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%")
print("\n\n")
print("Please enter the name of the item that you want to add.")
print("Press ENTER to return to the main menu.\n")

#here input fuction takes the input from the user from the consloe and stored in to the item.
item = input("\nItem: ")
if len(item) > 0:   #item lenth should be > zero
sl.append(item)   # we added this item to s1
print("Item added :-)")   # giving an acknowledment for added item succssfully.
saveList()       # invokes the saveList it will save the list of data entered by the user.
time.sleep(1)   #it will wait one second and again invokes the addScreen method. sleep method suspends execution of the current thread for a given number of seconds.
addScreen()
else:
mainScreen()

def viewScreen():
os.system('cls') # for linux 'clear'
print("%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%")
print(" VIEW SCREEN ")
print("%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%")
print("\n\n")
# we print each and every item from the s1 by using for loop.
for item in sl:
print(item)

print("\n\n")
print("Press enter to return to the main menu")  
input()   #here we are not save input from the consloe. We can press enter or any key
mainScreen()   #invokes main menu

def deleteScreen():
global sl
os.system('cls') # for linux 'clear'
print("%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%")
print(" DELETE SCREEN ")
print("%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%")
count = 0

#here we display the all the list from s1 including with numbers.
#for that we took one count veriable and prits the items along with count number.
for item in sl:
print(count, " - ", item)
count = count + 1   # increasing count value
print("What number to delete?")

#choice is the number of item.
choice = input("number: ")

#as we know try hndle the exceptions.
if len(choice) > 0:
try:
del sl[int(choice)]   #our s1 is an array string type. So based on number we can delete the item from the s1.
print("Item deleted...")
saveList()   # after delete item from the list we should save the current list in s1.
time.sleep(1)   # suspend one second.
except:
print("Invalid number")   # if we gave invalid number then try passed to except: and it prints the Invalid number
time.sleep(1)
deleteScreen()   # again It invokes the delete screen menu.

else:
mainScreen()       # invokes main screen.

# function for save the data in to the s1.
def saveList():
       # we open file shopping2.txt file and we use the mode of w -> writing mode
       # user able to do write the data in to the file
f = open("shopping2.txt", "w")
     
   #we save the item data in to file from the s1 array
for item in sl:
f.write(item+"\n") # write method is used to write the data in to the file.
f.close()   # we should close the file after writing.

#First program will start from here.   

mainScreen()

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