(Python) How can I let a user open a text file and then change an integer / number

Question

I've asked a similar question but to no avail.

I am a novice programming student and I've only been taught some basic techniques. Part of a task is to create a recipe program which I've mostly done, there is just one part preventing me from finishing.

I am supposed to allow a user to call a previously created text file (I've done this bit), then after this the contents of this file should be displayed for them to see (I've also done this bit), however the user should be able to recalculate the servings and therefore change the quantity of the ingredients. So if the user entered: "I want 2 servings" and the original quantity for 1 serving was 100g it should now output 200g.

It is really frustrating me and my teacher expects this work tomorrow. Below is what I am supposed to allow the user to do.

The user should be able to retrieve the recipe and have the ingredients recalculated for a different number of people.

• The program should ask the user to input the number of people.

• The program should output:

• the recipe name

• the new number of people

• the revised quantities with units for this number of people.

I will post my actual code below to show what I have done so far, which is to allow a user to view and make a new recipe. But the revised quantities bit is missing.

I apologise if the code is messy or unorganised, I am new to this.

Code so far:

#!/usr/bin/env python

import time

def start():

    while True:

        user_input = input("\nWhat would you like to do? " "\n 1) - Enter N to enter a new recipe. \n 2 - Enter V to view an exisiting recipe, \n 3 - Enter E - to edit a recipe to your liking. \n 4 - Or enter quit to halt the program " "\n ")

        if user_input == "N":
            print("\nOkay, it looks like you want to create a new recipe. Give me a moment..." "\n")
            time.sleep(1.5)
            new_recipe()

        elif user_input == "V":
            print("\nOkay, Let's proceed to let you view an existing recipe stored on the computer")
            time.sleep(1.5)
            exist_recipe()

        elif user_input == "E":
            print("\nOkay, it looks like you want to edit a recipe's servings. Let's proceed ")
            time.sleep(1.5)
            modify_recipe()

        elif user_input == "quit":
            return

        else:
            print("\nThat is not a valid command, please try again with the commands allowed ")


def new_recipe():
    new_recipe = input("Please enter the name of the new recipe you wish to add! ")
    recipe_data = open(new_recipe, 'w')
    ingredients = input("Enter the number of ingredients ")
    servings = input("Enter the servings required for this recipe ")

    for n in range (1,int(ingredients)+1):

        ingredient = input("Enter the name of the ingredient ")
        recipe_data.write("\nIngrendient # " +str(n)+": \n")
        print("\n")
        recipe_data.write(ingredient)
        recipe_data.write("\n")
        quantities = input("Enter the quantity needed for this ingredient ")
        print("\n")
        recipe_data.write(quantities)
        recipe_data.write("\n")
        unit = input("Please enter the unit for this quantity (i.e. g, kg) ")
        recipe_data.write(unit)
        print("\n")

    for n in range (1,int(ingredients)+1):
        steps = input("\nEnter step " + str(n)+ ": ")
        print("\n")
        recipe_data.write("\nStep " +str(n) + " is to: \n")
        recipe_data.write("\n")
        recipe_data.write(steps)
    recipe_data.close()

def exist_recipe():
    choice_exist= input("\nOkay, it looks like you want to view an existing recipe. Please enter the name of the recipe required. ")
    exist_recipe = open(choice_exist, "r+")
    print("\nThis recipe makes " + choice_exist)
    print(exist_recipe.read())
    time.sleep(1)

def modify_recipe():
    choice_exist = input("\nOkay, it looks like you want to modify a recipe. Please enter the name of this recipe ")
    exist_recipe = open(choice_exist, "r+")    
    servrequire = int(input("Please enter how many servings you would like "))


start()

EDIT:

Below is an example creation of a text file (recipe) and it's output (the file is called bread.txt) Note the outputs are a bit messy, I will fix that once I can get the core of the program to work.

Creating a recipe

What would you like to do? 
 1) - Enter N to enter a new recipe. 
 2 - Enter V to view an exisiting recipe, 
 3 - Enter E - to edit a recipe to your liking. 
 4 - Or enter quit to halt the program 
 N

Okay, it looks like you want to create a new recipe. Give me a moment...

Please enter the name of the new recipe you wish to add! bread.txt
Enter the number of ingredients 3
Enter the servings required for this recipe 1
Enter the name of the ingredient flour


Enter the quantity needed for this ingredient 300


Please enter the unit for this quantity (i.e. g, kg) g


Enter the name of the ingredient salt


Enter the quantity needed for this ingredient 50


Please enter the unit for this quantity (i.e. g, kg) g


Enter the name of the ingredient water


Enter the quantity needed for this ingredient 1


Please enter the unit for this quantity (i.e. g, kg) l



Enter step 1: pour all ingredients into a bowl



Enter step 2: mix together



Enter step 3: put in a bread tin and bake

Viewing a recipe

What would you like to do? 
 1) - Enter N to enter a new recipe. 
 2 - Enter V to view an exisiting recipe, 
 3 - Enter E - to edit a recipe to your liking. 
 4 - Or enter quit to halt the program 
 V

Okay, Let's proceed to let you view an existing recipe stored on the computer

Okay, it looks like you want to view an existing recipe. Please enter the name of the recipe required. bread.txt

This recipe makes bread.txt

Ingrendient # 1: 
flour
300
g
Ingrendient # 2: 
salt
50
g
Ingrendient # 3: 
water
1
l
Step 1 is to: 

pour all ingredients into a bowl
Step 2 is to: 

mix together
Step 3 is to: 

put in a bread tin and bake

And here is the output if you enter V:

This recipe makes bread.txt

Ingrendient # 1: 
flour
300
g
Ingrendient # 2: 
salt
50
g
Ingrendient # 3: 
water
1
l
Step 1 is to: 

pour all ingredients into a bowl
Step 2 is to: 

mix together
Step 3 is to: 

put in a bread tin and bake

I look forward to your replies.

Answer 1

It looks like your recipe files look like this:

Ingrendient # N: 
{INGREDIENT}
{AMOUNT}
{METRIC}
...
(After N ingredients...)
Step N: 
{INSTRUCTIONS}

So basically you want to read four lines at a time, discard the first, then assign the rest to something useful.

with open(path_to_recipe) as infile:
    ingredients = []
    while True:
        try:
            sentinel = next(infile) # skip a line
            if sentinel.startswith("Step"):
                # we're past the ingredients, so
                break
            name = next(infile)
            amount = next(infile)
            metric = next(infile)
        except StopIteration:
            # you've reached the end of the file
            break
        ingredients.append({'name':name, 'amount':float(amount), 'metric':metric})
        # use a dictionary for easier access

When we exit the with block, ingredients will be a list of dictionaries that can be used as follows:

for ingredient in ingredients:
    scaled_volume = ingredient['amount'] * scale # double portions? etc...
    print(scaled_volume, ingredient['metric'], " ", ingredient['name'])
# # RESULT IS:
300g flour
50g salt
1l water

You should be able to leverage all that to finish your assignment!