Python餐厅提示计算器

Question

So I am a complete newbie to coding and need some help. I am trying to create a code for a tip calculator but am not quite sure where I am going with it. I was never in class to be taught by my teacher so I am going out on a whim with this. There is a requirement to have a class but I know I am going about it the wrong way. Any help is appreciated. This is what I have so far:

import decimal

class Tip:

    def __init__(self):
        self.tip=0

    def __str__(self):
        return 'Tip['+str(self.sub_total)+' * '+str(self.percentage)+']'

    def sub_total():
        self.sub_total = input()

    def percentage():
        self.percentage = input()

    def get_tip(percentage, sub_total):
        self.percentage = decimal.Decimal(percentage)
        self.sub_total = decimal.Decimal(sub_total)
        self.tip = ((sub_total * percentage) / 100)
        self.total = (sub_total + tip)
        return self.__str__()

t = Tip()

print ("How much is the bill?")
t.sub_total()

print ("What percentage should the tip be?")
t.percentage()

print (t.get_tip())

Everytime I run it I get this:

get_tip() takes exactly 2 arguments (1 given)

Like I said, I am kindof making it up as I go and any help is appreciated.

Answer 1

Hoo boy, there's a lot of things to cover. I'll try to get it all, but will start with working code.

class Bill(object):  # note: not Tip!
    def __init__(self, sub_total):
        self.sub_total = sub_total

    def calculate_tip(self, tip_pct):
        return self.sub_total * tip_pct

    def calculate_total(self, tip_pct):
        return self.sub_total * (1 + tip_pct)

This defines a Bill object. If we want to use it, we could do:

subtotal = float(raw_input("Bill subtotal: "))
b = Bill(subtotal)

Then to get the tip we could do

tip_percentage = float(raw_input("Tip Percent (15% --> 0.15): "))
tip_amt = b.calculate_tip(tip_percentage)

And to get the grand total:

grand_total = b.calculate_total(tip_percentage)

Here's where you went wrong:

Your original class, for reference, looks like:

class Tip:

    def __init__(self,sub_total,percentage):
        self.tip= (sub_total * percentage)

    def __str__(self):
        return 'Tip['+str(sub_total)+' * '+str(percentage)+']'

    def sub_total():
        sub_total = input()

    def percentage():
        percentage = input()

    def get_tip(percentage, sub_total):
        percentage = decimal.Decimal(percentage)
        sub_total = decimal.Decimal(sub_total)
        tip = ((sub_total * percentage) / 100)
        total = (sub_total + tip)
        return Tip(total)

We'll talk about it method by method.

1. __init__

This one is great! It means you create a Tip object by passing the sub_total and the percentage (as a ratio to 1) in the constructor, so t = Tip(15.00, 0.15) is a 15% tip on $15. Hooray!

2. __str__

Only briefly going to go into this one, other than to mention that this looks more like a __repr__ than a __str__ and you should use ( / ) instead of [ / ] . Remember that sub_total and percentage aren't attributes of the object -- they're just arguments that were passed to its constructor. You can't reference them here if you don't save them in the __init__ method.

3. sub_total

First of all, you can't call this since it doesn't have a self argument. Second of all it doesn't do anything even if you could. sub_total = input() gets user input, then throws it away.

4. percentage

See above

5. get_tip

You're missing a self argument, again, but I'll talk about it as if it was get_tip(self, percentage, sub_total) . You call this by using your already-created Tip object (remember above when we did t = Tip(15, 0.15) ?) and calling it with the arguments that you probably passed the constructor. In other words:

t = Tip(15, 0.15)  # 15% tip on $15
t.get_tip(0.15, 15)  # ...15% tip on $15, but the grand total...

It doesn't make a whole lot of sense as a function. Especially since half your work is already done for you and saved in self.tip . If this is the pattern you wanted to use for your object, you could do something like:

class Tip(object):
    def __init__(self, sub_total, tip_pct):
        self.sub_total = sub_total
        self.tip_pct = tip_pct
        # saving these as attributes so we can use them later
        self.grand_total = self.sub_total * (1 + self.tip_pct)
        self.tip_amt = self.sub_total * self.tip_pct

But that really looks more like a series of functions to me, than something that needs to be saved as an object!

Nota Bene

Remember that classes are here to provide a state for your code to run in. In this case, the only state you can really apply is "How much to tip," so I suppose you could do the reverse of this and do something like:

t = Tip(0.15)
t.calculate_total(amt_of_bill)

But it seems silly to me. You could maybe make a factory function that does something like:

def tip(tip_pct):
    def wrapped(bill_amt):
        return bill_amt * (1 + tip_pct)
    return wrapped

But that's a little advanced for where you're at.

Answer 2

You need to create a tip calculator object first. Then, I see that the object could take the input by themselves. I think the following code will fix your problem (or at least get you closer to the correct answer).

So try this:

class Tip:

    def __init__(self):
        self.tip=0

    def __str__(self):
        return 'Tip['+str(self.sub_total)+' * '+str(self.percentage)+']'

    def sub_total():
        self.sub_total = input()

    def percentage():
        self.percentage = input()

    def get_tip(percentage, sub_total):
        self.percentage = decimal.Decimal(percentage)
        self.sub_total = decimal.Decimal(sub_total)
        self.tip = ((sub_total * percentage) / 100)
        self.total = (sub_total + tip)
        return self.__str__()

t = Tip()

print ("How much is the bill?")
t.sub_total()

print ("What percentage should the tip be?")
t.percentage()

print (t.get_tip())

Answer 3

There are a few errors in your program. The most blatent, the one creating the text you see, is the missing parenthesis with the get_tip call. You are literally printing the function , not the result.

However, this won't be enough by itself. There are a bunch more and here's a list of them:

• You don't seem to have an handle of OOP, and it is not really necessary for this assignment. You can take the functions out of the class.
• All the functions are unnecessary, except for get_tip .
• The print statements can go inside the inputs as in input("foo: ")
• You need to save each answer to a different variable.
• No parens needed with print in python2

Here is my take on the problem:

def get_tip(percentage, sub_total):
    tip = ((sub_total * percentage) / 100)
    total = (sub_total + tip)
    return total

sub_total = input("How much is the bill?")

percentage = input("What percentage should the tip be?")

print get_tip(percentage, sub_total)

There. Mcuh simpler.

Answer 4

It's been a bit since I've actually used Python, but from what I can see you'd want to actually call for an instance of the class Tip instead. So instead of just referring to Tip, you say x=Tip() instead.

The use of input is a little wrong too. You're calling to answer twice so nothing is really happening there. You already have two methods to read input, so you'd use those to get the sub total and percentage instead.

This should work better:

import decimal

class Tip:

    def __init__(self,sub_total,percentage):
        self.tip= (sub_total * percentage)

    def __str__(self):
        return 'Tip['+str(sub_total)+' * '+str(percentage)+']'

    def sub_total():
        sub_total = input()

    def percentage():
        percentage = input()

    def get_tip(percentage, sub_total):
        percentage = decimal.Decimal(percentage)
        sub_total = decimal.Decimal(sub_total)
        tip = ((sub_total * percentage) / 100)
        total = (sub_total + tip)
        return Tip(total)

    t = Tip()

    print ("How much is the bill?")
    t.sub_total()

    print ("What percentage should the tip be?")
    t.percentage()

    print (t.get_tip)