python study note

Catalog

Comments and quotation marks are used 、 code

Data types and variables

lambda、zip、map、reduce、enumerate function

_xx、__xxx、__xxx__ The difference between

class 、 Function definition 、 exception handling

IO Programming

Comments and quotation marks are used 、 code

# encoding=utf-8 perhaps # -*- utf-8 -*-

Single-line comments ：#

Multiline comment ：''' ''' perhaps """ """

character string ： Single quotation marks ：'' Double quotes ：" " Three quotes ：''' ''' or """ """, Three quotes support line wrapping

escape ：r'',r Do not escape string

Data types and variables

Integers （int）、 Floating point numbers （float）、 The plural （complex）、 character string （str)、 Boolean and null values

test_int = 1
test_float = 1.0
test_str = "abc"
test_complex = complex(1,2)
test_bool_1 = True
test_bool_2 = False
test_none = None

Tuples （tuple）、 list （list）、 Dictionaries （dict）、 aggregate （set）

# Tuples are immutable
test_tupble = (1,2,3)
test_list = [1,2,3]
test_dict = {"a":1,"b":2}
# Empty collection must use test_set = set(),test_set = {} Will resolve to an empty dictionary
test_set = {"a","b","c"} 

Correlation function description

'''
Array sorting ：sorted
The length can be used ：len()
String formatting ："{},{}".format("a","b")
Insert elements ： The order of a （list）:append
Non sequential concept （set）:add
Class's own function （__xxx__ Format , It's usually a function , So when calling, it is usually __xxx__()）：__len__()
'''
test_tuple = (1,2,3)
print(len(test_tuple))
print(test_tuple.__len__())

lambda、zip、map、reduce、enumerate function

from functools import reduce
test_list_1 = ['a','b','c']
test_list_2 = [1,2,3]
# zip
for index,value in zip(test_list_2,test_list_1):
print(index,value)
# enumerate
for index,value in enumerate(test_list_1):
print(index,value)
#reduce
test_reduce = reduce(lambda x,y:x+y,test_list_2)
print(test_reduce)
#lambda map
test_map = map(lambda x:x*2,test_list_2)

_xx、__xxx、__xxx__ The difference between

class TestClass():
'''
_xx:Python There is no real private method in . To achieve something similar to c++ Private methods in , You can add a before a method or property of a class “_” Underline , This means that the method or property should not be called , It doesn't belong to API.
__xx: It is not used to identify that a method or property is private , The real function is to avoid subclasses covering its contents . When compiled, it will become _A__method()
__XX__: be used for python call , Do not use
'''
def __init__(self):
self._test_a = 1
def __method(self):
print("This method from A！")
def method(self):
self.__method()

class 、 Function definition 、 exception handling

class TestClass():
def __init__(self):
self.test_x = 1
def test_exception(self):
try:
print("aaa")
raise ValueError("value error")
except ValueError as e:
print(e)
finally:
print("try except finally example!")
test_class = TestClass()
test_class.test_exception()

IO Programming

File read and write

file_name = "test.txt"
try:
f = open(file_name,"w+",encoding="utf-8")
for line in f.readlines():
print(line)
test_write = " Test write data "
f.write(test_write)
f.close()
except Exception as e:
print("exception:",e)
finally:
if f:
f.close()
try:
with open(file_name,"w+",encoding='utf-8') as f:
for line in f.readlines():
print(line)
except Exception as e:
print("exception:",e)

serialize ：joblib and pickle

#joblib sklearn Self contained , More efficient ,joblib There is no function to sequence into strings
import joblib
import pickle
file_path = "xxxxx"
joblib.load(file_path)
joblib.dump(file_path)
#pickle
f = open("file_path",'rb')
d = pickle.load(f)
f.close()
# Store in file
f = open("file_path","wb")
pickle.dump(d,f)
f.close()
#dumps Serialize to string
d= dict(name="bob",age=20)
d_b = pickle.dumps(d)
#
d = pickle.loads(d_b)

os and sys modular

import os
import sys
# os Refers to operating system related , There is , For example, file path 、 Catalog
# sys Refers to system related , such as python Running path of , The path of the library
os.path.abspath(".")
sys.path.append("..")
sys.path

Common built-in modules