Continuing from last night's [Introduction to Data Scientists] Python Basics ♬ Functions and Anonymous Functions, etc., we will talk about functions and classes. 【Caution】 ["Data Scientist Training Course at the University of Tokyo"](https://www.amazon.co.jp/%E6%9D%B1%E4%BA%AC%E5%A4%A7%E5%AD%A6%E3 % 81% AE% E3% 83% 87% E3% 83% BC% E3% 82% BF% E3% 82% B5% E3% 82% A4% E3% 82% A8% E3% 83% B3% E3% 83 % 86% E3% 82% A3% E3% 82% B9% E3% 83% 88% E8% 82% B2% E6% 88% 90% E8% AC% 9B% E5% BA% A7-Python% E3% 81 % A7% E6% 89% 8B% E3% 82% 92% E5% 8B% 95% E3% 81% 8B% E3% 81% 97% E3% 81% A6% E5% AD% A6% E3% 81% B6 % E3% 83% 87% E2% 80% 95% E3% 82% BF% E5% 88% 86% E6% 9E% 90-% E5% A1% 9A% E6% 9C% AC% E9% 82% A6% I will read E5% B0% 8A / dp / 4839965250 / ref = tmm_pap_swatch_0? _ Encoding = UTF8 & qid = & sr =) and summarize the parts that I have some doubts or find useful. Therefore, I think the synopsis will be straightforward, but please read it, thinking that the content has nothing to do with this book.
This chapter focuses on the mechanism of python function calls and the differences between class notation and functions. For the mechanism of function call, refer to the following. 【reference】 Module function call @PyQ
Create an instance from the class. We'll leave this book a bit to show the similarities between function calls, class declarations, and instance execution.
Functions are sometimes used in one PG, but when trying to write a complicated PG, the function is saved and used as a Package with a structured directory structure. In that case, python has an important mechanism.
That is, if you execute the following code with > python calc_add.py, it will work in the following order.
① Two function definitions are made
② The module name calc_add is assigned to __name__
③ The print statement is executed
④ The ʻif statement is True, and the following two print` statements are executed.
calc_add.py
def calc_add(a, b):
return a + b
def calc_multi(a, b):
return a * b
print('__name__:', __name__)
if __name__ == '__main__':
print(calc_add(5,3))
print(calc_multi(5, 3))
result
__name__: __main__
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main.pyIn this case, run > python main.py
(1) Read the two functions calc_add and calc_multi from calc_add.py by the first declaration statement. At this time, as you can see from the output, the above calc_add.py is executed, the print statement is executed, and __name__: calc_add is output. ʻIf statement is False (__ name__ = calc_add), so it will not be executed ② Next, the print statement of main.py is executed. ③ Since the ʻif statement of main.py is True, the following two print statements are executed.
With this mechanism, you can call a function and use it.
④ Therefore, it is necessary to include the notation ʻif name =='main':`. However, it is not essential when calling and using it.
main.py
from calc_add import calc_add, calc_multi
print('__name__2:', __name__)
if __name__ == '__main__':
print(calc_add(5,3))
print(calc_multi(5, 3))
result
__name__: calc_add
__name__2: __main__
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** Note) print ('__ name__:', __name__) is included to explain the mechanism and is not usually required **
class
The class looks the same as the function.
However, declare class.
Then, as you can see in the if statement, the class defines the instance and then calls and uses the function defined in the class.
This mechanism is called object-oriented.
That is, it is a mechanism that generates many instances from class and executes them.
The features of the class definition are as follows.
① Declare class
(2) Define the constructor def __init __ (self, x, y):. The variable self is mandatory and defined (the variable self is special, but it took me a while to think it was just one of the variables). The arguments x and y define what is needed at any given time.
【reference】
What is Python self? Explanation of usage and precautions
About self
-Self is not described as an argument when declaring instance
・ Self is a class variable
・ Can be used for class inheritance
-If both the class variable and the instance variable have values, the instance variable is given priority for reference.
③ Constructor def __init __ (self, x, y): is the code that works first when the instance of the class is defined.
④ Define other necessary functions.
⑤ Execute necessary processing like ʻinstance.calc_add () ⑥ ʻif __name__ =='__main__': is written for the same reason as the function, but it is not essential when calling and using it, so many classes do not have this if statement or execution statement.
** Note) print ('__ name__:', __name__) is included to explain the mechanism and is not usually required **
calc_class.py
class MyCalcClass:
def __init__(self,x,y):
self.x = x
self.y = y
def calc_add1(self, a, b):
return a + b
def calc_add2(self):
return self.x + self.y
def calc_multi(self, a, b):
return a * b
print('__name__:', __name__)
if __name__ == '__main__':
instance_1 = MyCalcClass(1,2)
instance_2 = MyCalcClass(5,10)
print(instance_1.calc_add1(5,3))
print(instance_1.calc_add2())
print(instance_1.calc_multi(5, 3))
instance_1.calc_print(5)
>python calc_class.py
result
It is as follows, but you can see that the result is calculated depending on the initial value of instance1.
If the if statement part is deleted, only __name__: __main__ is output.
__name__: __main__
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data:5:Value of y 2
main.pymain_class.py
from calc_class import MyCalcClass
print('__name__2:', __name__)
if __name__ == '__main__':
instance_1 = MyCalcClass(1,2)
instance_2 = MyCalcClass(5,10)
print(instance_1.calc_add1(5,3))
print(instance_1.calc_add2())
print(instance_1.calc_multi(5, 3))
instance_1.calc_print(5)
result
>python main_class.py
Of course, the result is the same as ↑. However, as with the function, __name__: calc_class is output.
That is, the name of the called file is entered in __name__, and __main__ is entered in the case of itself.
__name__: calc_class
__name__2: __main__
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data:5:Value of y 2
・ I compared the function call and the class. -Define a class, call it, and execute the instance
・ It's just before writing general python code ・ This book ends the basics of python in this section, but the missing parts will be supplemented in future sections (in a sense, this book will continue to explain the code using various Lib of python).
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