My child "Ogyaaogyaa !! Don't understand Python at all !!"
I said, "Oh, my child, who is a beginner in Python, doesn't understand Python and I don't have it today ..."
I said, "Everyone can't program Python quickly and easily, but I don't think that the super convenient functions that are so popular are not known. Moreover, when I try to use the convenient functions, I don't understand the meaning. I don't know. "
I said, "So this time, I'll introduce a grammar that is relatively new but doesn't seem to be well known! Everyone seems to be aiming for a complete understanding of Python!"
-[Type hint](# type hint)
I said, "At first, the type hints added in version 3.5!"
I "Do you all know that Python is a ** dynamically typed ** language?"
I said, "** Dynamic typing ** means that it will be automatically determined even if you don't specify the type!"
I said, "For example, in the ** statically typed ** language, variables are declared like this."
var name str = "nokonoko" //str type
var age int = 5 //int type
I "I wonder if I should decide in advance what value will be entered in the variable. If I enter a type other than the specified one, an error will occur."
I "On the other hand, Python ..."
name = "nokonoko" #str type
age = 5 #int type
I said, "Even if you don't bother to declare the type name like this, you can just declare the variable normally and decide the type without permission! Python is convenient!"
I said, "If you look at this, ** static typing ** is just annoying ..." But why is there still a statically typed language (rather, static typing is more popular ...?) ... because it has merit. Maybe it's roughly this much. "
--Speed: The operation is fast because the type determination has already been completed on the code. --Safety: The presence of the type reduces the probability of a seemingly unknown bug occurring. --Easy to read: It's hard to write, but it's easy to guess the behavior because the types of arguments and return values are self-explanatory.
I said, "** Small scale **, if you move it for the time being, it's OK **, ** speed doesn't matter **, ** if you develop by yourself **, you don't care about the type, but usually it does. It's not. "
I said, "It seems that Python was born to write simple scripts in the first place, but from such a popular situation, it seems that there was a strong request for Python to be statically typed. Because it's difficult to do ... I was born with a ** type hint **! "
I said, "It's used like this."
def hello(name: str) -> str:
return f"Hello {name}"
I said, "You can set the type of variables and function arguments / return values! Now when you write code using IDE etc., you will be warned when you take a variable of different type as an argument. so!!"
I said, "But it's not really a typed language, it can be executed, so be careful!"
--Python is a dynamically typed language, so the type is automatically determined. --Type hints allow you to specify types for variables and functions --However, it is just a type ** hint ** and can be executed without causing a compile error.
Reference: typing --- support for type hints
Docstring
I said, "Next is Docstring! This is also a useful function! Let's see what it is!"
def hello(name):
"""Say hello to the person you put in the argument"""
return f"Hello {name}"
I said, "You can embed a document in your code by putting a string enclosed in three quotation marks in a function (or a class module) like this!"
I said, "This is what makes it different from just a comment, but the string embedded here is not stored in the object's special method __doc__. "
I said, "That's what you can do withhelp ()in interactive mode to see the documentation, or Sphinx. If you use, it will automatically create a document and you will get a lot of deals! It's a bit different from just a comment. "
>>> help(hello)
Help on function hello in module __main__:
hello(name)
Say hello to the person you put in the argument
I said, "More !!!!!! By embedding multiple lines of Docstring, you can write the type hints I explained earlier in Docstring!"
I "like this!"
def hello(name):
"""Say hello to the person you put in the argument
Args:
name(str):The name of the person you want to say hello to
Returns:
str:Greetings
"""
return f"Hello {name}"
I said, "You can check the type with IDE etc. just like you put the type hint with this!"
I said, "The one I wrote above is calledGoogle style, but I can write various things other than the arguments and return values, and there are other ways to write it in the first place, so if you're curious, check it out! "
I said, "It's convenient for developing with a large number of people, so everyone should try it!"
--By embedding a string enclosed in three quotation marks in a function, class, or module, the string is stored in the special method __doc__.
--You will be able to use useful functions such as help () and reference in the IDE that will speed up development.
--Type hints can be added by writing multiple lines
Reference: PEP 257 --Docstring Conventions
f-string
I "Next is the f-string (f string and!) Added in version 3.6"
I said, "There are about two ways to embed variables in a character string.
>>> name = "nokonoko"
>>> age = 5
>>> print("{}Is{}I'm old".format(name, age))
nokonoko is 5 years old
I "toka"
>>> print("%s is%s years old" % (name, age))
nokonoko is 5 years old
I "Tokayana."
I said, "That way ... it's old."
I "I can't do it like this now!"
>>> print(f"{name}Is{age}I'm old")
nokonoko is 5 years old
I said, "Doya. I've erased all the methods and symbols I don't understand and made it simpler!"
I said, "More. You can do this from Python 3.8."
>>> print(f"name={name}, age={age}") # 3.Up to 7
name=nokonoko, age=5
>>> print(f"{name=}, {age=}") # 3.From 8
name='nokonoko', age=5
I said, "By putting variables and = in {}, the variable names are automatically displayed! It's useful when debugging! "
I said, "Let's use this positively when creating a new project from convenience!"
--There are different types of string embedding, but the most convenient is the latest ** f-string **. --Since Python 3.8, you can also embed variable names, which is even more convenient.
Reference: 2.4.3. Formatted string literals
I "Next is the ** walrus operator ** added in version 3.8!"
I said, "The walrus operator is the assignment operator: = , and it seems that it came to be called because it looks like a walrus's eyes and fangs when viewed from the side!"
I "... well, I can't see it !!!"
I said, "A function that allows you to leave it for the time being and assign it to a variable in an if statement or for statement! It's like this!"
# 3.Up to 7
>>> name = "nokonoko"
>>> if name == "nokonoko":
... print("handsome, eh")
... else:
... print("It's not handsome")
handsome, eh
# 3.From 8
if name := "nokonoko" == "nokonoko":
... print("handsome, eh")
... else:
... print("It's not handsome")
handsome, eh
I said, "Well, it's a natural result."
I said, "It's a function that allows you to assign to variables in conditional expressions like this, and it's an excellent one that can shorten redundant expressions."
I said, "However, this is not so well known because of its really new features, and depending on how it is used, it may reduce readability, so use it with caution!"
I said, "Especially in Python, ** if statements and for statements do not create a local scope **, so be careful!"
-** Walrus operator ** is an operator that can be assigned even in conditional expressions --Be careful about readability when using
Reference: PEP 572 --Assignment Expressions
I "Next is the inclusion notation!"
I said, "This is a function to simply create an object (having a reference to another object) that stores multiple values such as a variable called ** container object **."
I said, "The most commonly used list comprehension is."
#Create a new list
>>> numbers = []
>>> for i in range(10):
... numbers.append(i)
>>> numbers
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
#If you use the comprehension notation, it will be like this
>>> numbers = [i for i in range(10)]
>>> numbers
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
I said, "It's an excellent thing that makes it possible to define an array using a for statement in one line!"
I said, "And you can also embed an if statement!"
#Ordinary for statement
>>> numbers = []
>>> for i in range(10):
... if i % 2 == 0:
... numbers.append(i)
...
>>> numbers
[0, 2, 4, 6, 8]
#Comprehension notation
>>> numbers = [i for i in range(10) if i % 2 == 0]
>>> numbers
[0, 2, 4, 6, 8]
I said, "Furthermore, unlike the for statement, it closes the scope!"
#Ordinary for statement
>>> numbers = []
>>> for i in range(10):
... numbers.append(i)
#The variable i defined in the for statement can be referenced.
>>> i
９
#Comprehension notation
>>> numbers = [i for i in range(10)]
#Exception occurs as variable i is undefined
>>> i
Traceback (most recent call last):
File "<input>", line 1, in <module>
NameError: name 'i' is not defined
I said, "Because it prevents bugs, use inclusion notation as much as possible when creating a new list!"
I said, "By the way, the comprehension can't be used for anything other than lists! I'll introduce that too!"
>>> dict_obj = {str(i): i for i in range(10)}
>>> dict_obj
{'0': 0, '1': 1, '2': 2, '3': 3, '4': 4, '5': 5, '6': 6, '7': 7, '8': 8, '9': 9}
>>> set_obj = {i for i in range(10)}
>>> set_obj
{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
I said, "From the flow so far, I wonder if the tuple inclusion notation can be completed by changing the enclosing symbol to(), but this is a little exception, and a generator can be created. Be careful because it is complicated!"
gen_obj = (i for i in range(10))
gen_obj
<generator object <genexpr> at 0x10df04580>
I said, "There are various inclusion notations, and all of them are convenient, so please use them!"
--Comprehension is a function to simply create a container object. --Since the scope is closed, it is difficult to create bugs. --You can also create container objects other than lists --Deep nesting reduces readability, so be careful
Reference: 5. Data Structures
I said, "Next is a generator! This is a function that has been around for a long time, but it's a function that beginners don't really understand how to use. If you don't bother to make a generator, you can make a list ..."
I thought, "I thought, but I feel like I'll be a big success in the following two points."
--When you want to make an infinite loop without stopping the process --When you want to handle a large amount of text data
I "for example ..."
while True:
print("Returns a value")
I said, "When I write code, I immediately enter an infinite loop. It's possible that the system will continue to be consumed and the system will go down ... so I'm usually careful not to do it."
I said, "The same thing may happen even if you are limited to an infinite loop, or if you make a huge list with heavy mathematical calculations."
I said, "But if you use the generator as below, you don't have to squeeze the memory from creating a new element until the next element is required (calling the special method __next__)! "
I said, "There are two ways to create a generator, specifically this way!"
#How to create a function
>>> def my_gen():
... x = 0
... while True:
... yield x
... x += 1
#The return value is generator
>>> my_gen()
<generator object my_gen at 0x10df04510>
>>> for i in my_gen():
... print(i)
0
1
2
3
...
#How to use a generator formula
>>> my_gen = (i for i in range(10000) if i % 2 == 0)
>>> for i in my_gen:
... print(i)
0
2
4
6
8
I said, "The return value of the generator is an iterator, so it can be used in a for statement!"
I said, "It seems to be very convenient when you want to read and process csv with 1 million records!"
I said, "By the way, the generator can also be converted to other container objects! But be careful as it can consume a lot of memory when it is created!"
>>> my_gen = (i for i in range(10000) if i % 2 == 0)
>>> my_list = list(my_gen)
>>> type(my_list)
<class 'list'>
>>> my_list
[0, 2, 4, 6, 8, 10, 12, 14, 16,...9992, 9994, 9996, 9998]
--The generator is an iterator that generates a value each time it is called --Not all values are expanded, so memory consumption can be reduced. --Convenient when handling large volumes of data
I said, "How did you do it! You got closer to a Python complete understanding man!"
My child "Ogyaaogyaa !! Python seems super easy !!"
I said, "Yeah. It seems that my child could understand Python completely. You in front of the screen will do your best to become a Python complete understanding man!"
Oshimai
Recommended Posts