A function, also known as a method, is a piece of code used to implement a specific function
Function to improve code reusability
Function must be called to execute
The variables defined in the function are local variables. Local variables can only be used in the function and cannot be used outside the function
A function does only one thing
import json def get_file_content(file_name): #Formal parameter #Enter parameter: pass in a file name #Return: the contents of the file are converted into a dictionary and returned with open(file_name, encoding='utf-8') as f: res = json.load(f) return res abc = get_file_content('stus.json') #The function call is executed only when the actual parameter is passed in here. The function has a return and needs to be received with a variable print(abc)
def write_file(filename,content): with open(filename,'w', encoding='utf-8') as f: #f.write(json.dumps(content)) json.dump(content,f,ensure_ascii=False,indent=4) dict = {'name':'wrp','age':'18'} write_file('wrp.json',dict)
''' //Homework: 1,Realize a commodity management procedure. #Output 1, add item 2, delete item 3, view item //Add item: //Name of product: xxx if the product already exists, it indicates that the product already exists //Price of goods: xxxx quantity can only be an integer greater than 0 //Product quantity: xxx, quantity can only be an integer greater than 0 2,Delete item: //Enter product name: iphone If the entered product name does not exist, you should be prompted that it does not exist 3,To view product information: //Enter product name: iphone: //Price: xxx //Quantity: xxx all: print Give all product information ''' FILENAME = 'products.json' import json def get_file_content(): with open(FILENAME, encoding='utf-8') as f: content = f.read() if len(content) > 0: res = json.loads(content) else: res = {} return res def write_file_content(dict): with open(FILENAME,'w',encoding='utf-8') as fw: json.dump(dict, fw, indent=4, ensure_ascii=False) def check_digit(st:str): if st.isdigit(): st = int(st) if st > 0: return st else: return 0 else: return 0 def add_product(): product_name = input("Please enter the product name:").strip() count = input("Please enter product quantity:").strip() price = input("Please enter commodity price:").strip() all_products = get_file_content() if check_digit(count) == 0: print("Illegal quantity input") elif check_digit(price) == 0: print("Illegal price input") elif product_name in all_products: print("Item already exists") else: all_products[product_name] = {"count":int(count),"price":int(price)} write_file_content(all_products) print("Add success") def del_product(): product_name = input("Please enter the product name to delete:").strip() all_products = get_file_content() if product_name in all_products: all_products.pop(product_name) print("Delete successful") write_file_content(all_products) else: print("Item does not exist") def show_product(): product_name = input("Please enter the product name to query:").strip() all_products = get_file_content() if product_name == 'all': print(all_products) elif product_name not in all_products: print("Item does not exist") else: print(all_products.get(product_name))
Copy
Shallow copy, memory address unchanged, point two objects to the same content,
Deep copy, which will regenerate the variables of the same content in memory
l = [1,1,1,2,3,4,5] l2 = l #Shallow copy #l2 = l.copy() #Shallow copy for i in l2: if i % 2 != 0: l.remove(i) print(l) #In this program, if you traverse and delete the same list, you will find that the result is inconsistent with the expectation, and the result is [1,2,4]. It is OK to use a deep copy
import copy l = [1,1,1,2,3,4,5] l2 = copy.deepcopy(l) # Deep copy for i in l2: if i % 2 != 0: l.remove(i) print(l)
Non null is true, non zero is true
name = input('Please enter a name:').strip() name = int(name) #False when entering 0 if name: print("Input correct") else: print("name Can not be empty")
Default parameters
import json def op_file_tojson(filename, dict=None): if dict: #If dict passes parameters, write json to the file with open(filename,'w',encoding='utf-8') as fw: json.dump(dict,fw) else: #If no parameter is passed, read json from the file f = open(filename, encoding='utf-8') content = f.read() if content: res = json.loads(content) else: res ={} f.close() return res
Check decimal type
def check_float(s): s = str(s) if s.count('.') == 1: s_split = s.split('.') left, right = s_split if left.isdigit() and right.isdigit(): return True elif left.startswith('-') and left[1:].isdigit and right.isdigit(): return True else: return False else: return False print(check_float('1.1'))
global variable
def te(): global a a = 5 def te1(): c = a + 5 return c res = te1() print(res) #The code will report an error. a defined in te() cannot be used before the function is called
money = 500 def t(consume): return money - consume def t1(money): return t(money) + money money = t1(money) print(money) #The result is 500
name = 'wangcai' def get_name(): global name name = 'hailong' print('1，In function name', name) def get_name2(): print('2，get_name2', name) get_name2() #wangcai get_name() #hailong print('3，Out of function name', name) #hailong
recursion
Recursion means that a function calls itself
Recursion up to 999 times
def te1(): num = int(input('please enter a number:')) if num%2==0: #Judge whether the input number is even return True #If it is even, the program exits and returns True print('Not even, please re-enter') return te1()#If not, continue to call yourself and input the value print(te1()) #Call test1
parameter
Position parameter
def db_connect(ip, user, password, db, port): print(ip) print(user) print(password) print(db) print(port) db_connect(user='abc', port=3306, db=1, ip='192.168.1.1', password='abcde') db_connect('192.168.1.1','root', db=2, password='123456', port=123) #db_connect(password='123456', user='abc', 2, '192.168.1.1', 3306) #The method is wrong. The location parameter must be written in the front and one-to-one correspondence. The key=value method must be written in the back
Variable parameters
def my(name, sex='female'): #name, required parameter, location parameter #sex, default parameter #Variable parameters #Key parameters pass def send_sms(*args): #Variable parameter #1. Not necessary #2. Put multiple elements in the tuple #3. Unlimited number of parameters #4. It is used when there are many parameters for p in args: print(p) send_sms() send_sms(123456) send_sms('123456','45678')
Key parameters
def send_sms2(**kwargs): #1. Not necessarily #2. Unlimited number of parameters #3.key=value format storage print(kwargs) send_sms2() send_sms2(name='xioahei',sex='nan') send_sms2(addr='Beijing',county='China',c='abc',f='kkk')
aggregate
Assemble, born to be heavy
Set out of order, list out of order
l = [1,1,2,2,3,3,3] res = set(l) #Convert list to set l = list(res) #set to list after de duplication print(res) print(l) set = {1,2,3} #set format jihe = set() #Define an empty collection xn=['tan','yang','liu','hei'] zdh=['tan','yang','liu','jun','long'] xn = set(xn) zdh = set(zdh) # res = xn.intersection(zdh) #intersect # res = xn & zdh #intersect res = xn.union(zdh) #Union and collection res = xn | zdh #Union and collection res = xn.difference(zdh) #Take the difference set, yes in A, no in B res = xn - zdh #Difference set res = xn.symmetric_difference(zdh) #Symmetric difference set, take the data that is not coincident between the two res = xn ^ zdh print(res)
import string l1 = set(string.ascii_lowercase) l2 = {'a','b','c'} print(l2.issubset(l1)) #Is l2 a subset of l2 print(l2.issuperset(l1)) #Is l2 the parent set of l2 print(l2.isdisjoint(l1)) #If there is intersection, if there is, then false, if there is no, then True l2.add('s') #Additive elements print(l2) print(l2.pop()) #Randomly delete an element l2.remove('a') #Delete specified element for l in l2: print(l)