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In python, if a person has the following code, will the 2 methods called automatically add? how does this work?
example:
def trip_cost(city,days):
return plane_ride_cost(city) + hotel_cost(days) + rental_car_cost(days)
Will hotel_cost(days) and rental_car_cost(days) both be added together when they are returned to trip_cost(city,days) ??
If the return values of the methods you invoke have a defined + operator they will add up.
If the 3 return numeric types (for example: float, int): yes
But if 2 return numeric and one returns a str: no
The return values may also be instances of objects defined by yourself which may have a defined + operator (which may or may not be compatible with numeric types or with strings)
Each function call [e.g. plane_ride_cost(city)] is evaluated and the results will be added together (in left to right order as +'s have equal precedence) then the overall result returned.
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How should I initialize multiple class arguments that came as chain and then calculate sum of them?
I've tried many ways but NOTHING
Do you have any idea?
>>> Chain(2.5)(2)(2)(2.5) # sum
9
>>> Chain(3)(1.5)(2)(3) # sum
9.5
In general, you'll want to add a __call__ method to your class so that calling an instance returns a new instance. Your class should also subclass the type matching the result you want.
In this specific case, the new instance could, for example, maintain a running sum of the initial value and all successive arguments.
class Chain(float):
def __call__(self, x):
return Chain(self + x)
Then
>>> Chain(2.5)
2.5
>>> Chain(2.5)(2)
4.5
>>> Chain(2.5)(2)(2)
6.5
>>> Chain(2.5)(2)(2)(2.5)
9.0
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Suppose I have two functions
def sum(a, b):
result = a + b
return result
and
def sum(a, b):
return a + b
From the point of view of good programming practices and software engineering, which solution is better? Return a value or assigning a value to a variable and then return? Why?
2nd option is good because it saves space of a variable but at times, we use more variables on purpose for the sake of clarity. We always have to maintain a good balance between clarity and space.
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Where are the python operators like +, -, * defined? I am a newbie, so please give a detailed answer to this question.
every Python class has built-in methods (can be recognized by the "__" in the beginning and end of their name) that define their behavior. for example, when using print() on an object, the built-in __str__ function is called, and it is different for every class.
you can override these functions with your own implementations.
here is a class named CarCollection:
class CarCollection():
def __init__(self, car_list):
self.cars_in_collection = car_list
now, say for example you want to add two collections together. using the "+" between two instances of this class will raise TypeError: unsupported operand type(s) for +: 'instance' and 'instance', so in order to add two collections together you need to override the __add__ function:
def __add__(self, other_car_collection):
return self.cars_in_collection + other.cars_in_collection
now when you add two collections together and print the result it will look like this:
first_collection = CarCollection(["subaru", "ferrari"])
second_collection = CarCollection(["fiat", "renault"])
print(second_collection + first_collection)
output: subaru, ferrari, fiat, renault
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I am new on Python.
I want to create a function with two vectors inside. I tried like this
def twovectors((velocity1,length1),(velocity2,length2)):
but I have a message error like
SyntaxError: invalid syntax.
Please, need help.
You cannot put tuple in the function definition as a parameter. Check Multiple Function Arguments or 8.6. Function definitions in the Python language reference.
Try something like this this:
def twovectors(vector1, vector2):
velocity1, length1 = vector1
velocity2, length2 = vector2
# Other code...
I used tuple unpacking to expand provided tuple arguments.
You write functions in python in this way :
def twovectors(velocity1, velocity2):
# You can get the length of those vectors after you get inside the function
len1, len2 = len(velocity1), len(velocity2)
// Your code here
return whateveryouwantto
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I have seen other people ask a question but the only answers I have seen simply explain that python doesn't have the same concept of pass by reference vs pass by value as languages like C do.
for example
x=[0]
def foo(x):
x[0] += 1
In the past, I have been using this work around but it seems very un-pythonic so I'm wondering if there is a better way to do this.
let's assume for what ever reason returning values won't work, like in the case where this code runs on a separate thread.
Some python objects are immutable (tuple, int, float, str, etc). As you have noted, you cannot modify these in-place.
The best workaround is to not try to fake passing by reference, instead you should assign the result. This is both easier to read and less error prone.
In your case, you could call:
x = 0
def f(x):
return x + 1
x = f(x)
If you truly need to fake passing by reference (and I don't see why you would need that), your solution works just fine, but keep in mind that you do not actually modify the object.
x = 0
x_list = [x]
print(id(x_list[0])) # 1844716176
def f(x_list):
x_list[0] += 1
f(x_list)
print(x) # 0, not modified
print(id(x_list[0])) # 1844716208