Python备忘录

发表于 2025-08-18 更新于 2025-08-19 分类于 Python 阅读次数：

简述
Python常用代码片段及相关工具类脚本

常用代码

# 字符串反转
Str = input("Please input String:\n")
RString = Str[::-1]
print("This String Reversal:\n%s" % RString)

 

# 首字母大写
my_string = "my name is chaitanya baweja"
new_string = my_string.title()
print(new_string)



# 在字符串中查找唯一元素
my_string = "aavvccccddddeee"
temp_set = set(my_string)
new_string = ''.join(temp_set)
print(new_string)


# 次打印字符串或列表
n = 3 # number of repetitions
my_string = "abcd"
my_list = [1,2,3]
print(my_string*n)
# abcdabcdabcd
print(my_list*n)
# [1,2,3,1,2,3,1,2,3]



# 列表推导式
original_list = [1,2,3,4]
new_list = [2*x for x in original_list]
print(new_list)
# [2,4,6,8]



# 变量交换
a = 1
b = 2
a, b = b, a
print(a) # 2
print(b) # 1



# 将字符串拆分为子字符串列表
string_1 = "My name is Chaitanya Baweja"
string_2 = "sample/ string 2"
print(string_1.split())
# ['My', 'name', 'is', 'Chaitanya', 'Baweja']
print(string_2.split('/'))
# ['sample', ' string 2']



# 将字符串列表组合成单个字符串
list_of_strings = ['My', 'name', 'is', 'Chaitanya', 'Baweja']
print(','.join(list_of_strings))
# My,name,is,Chaitanya,Baweja



# 检查回文字符串
my_string = "abcba"
if my_string == my_string[::-1]:
    print("palindrome")
else:
    print("not palindrome")
# Output
# palindrom



# 列表中的元素统计


from collections import Counter
my_list = ['a','a','b','b','b','c','d','d','d','d','d']
count = Counter(my_list) # defining a counter object
print(count) # Of all elements
# Counter({'d': 5, 'b': 3, 'a': 2, 'c': 1})
print(count['b']) # of individual element
# 3
print(count.most_common(1)) # most frequent element
# [('d', 5)]



# 查找两个字符串是否为字母
from collections import Counter
str_1, str_2, str_3 = "acbde", "abced", "abcda"
cnt_1, cnt_2, cnt_3  = Counter(str_1), Counter(str_2), Counter(str_3)
if cnt_1 == cnt_2:
    print('1 and 2 anagram')
if cnt_1 == cnt_3:
    print('1 and 3 anagram')



# 使用 try-except-else 块
a, b = 1,0
try:
    print(a/b)
    # exception raised when b is 0
except ZeroDivisionError:
    print("division by zero")
else:
    print("no exceptions raised")
finally:
    print("Run this always")



# 使用枚举获取索引 / 值对
my_list = ['a', 'b', 'c', 'd', 'e']
for index, value in enumerate(my_list):
    print('{0}: {1}'.format(index, value))

# 0: a
# 1: b
# 2: c
# 3: d
# 4: e



# 检查对象的内存使用情况
import sys
num = 21
print(sys.getsizeof(num))
# In Python 2, 24
# In Python 3, 28



# 合并两个字典
dict_1 = {'apple': 9, 'banana': 6}
dict_2 = {'banana': 4, 'orange': 8}
combined_dict = {dict_1, dict_2}
print(combined_dict)
# Output
# {'apple': 9, 'banana': 4, 'orange': 8}



# 执行一段代码所需的时间
import time
start_time = time.time()
a, b = 1,2
c = a+ b
end_time = time.time()
time_taken_in_micro = (end_time- start_time)*(106)
print(" Time taken in micro_seconds: {0} ms").format(time_taken_in_micro)



# 展平列表清单
from iteration_utilities import deepflatten
def flatten(l):
  return [item for sublist in l for item in sublist]
l = [[1,2,3],[3]]
print(flatten(l))
# [1, 2, 3, 3]

l = [[1,2,3],[4,[5],[6,7]],[8,[9,[10]]]]
print(list(deepflatten(l, depth=3)))
# [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]



# 从列表中随机取样
import random
my_list = ['a', 'b', 'c', 'd', 'e']
num_samples = 2
samples = random.sample(my_list,num_samples)
print(samples)
# [ 'a', 'e'] this will have any 2 random values



# 数字化
num = 123456
# using map
list_of_digits = list(map(int, str(num)))
print(list_of_digits)
# [1, 2, 3, 4, 5, 6]

list_of_digits = [int(x) for x in str(num)]
print(list_of_digits)
# [1, 2, 3, 4, 5, 6]



# 检查唯一性

def unique(l):
    if len(l)==len(set(l)):
        print("All elements are unique")
    else:
        print("List has duplicates")

unique([1,2,3,4])
# All elements are unique

unique([1,1,2,3])
# List has duplicates

操作数据库

Mysql 数据库

#!/usr/bin/env python
# -*- coding: UTF-8 -*-
import pymysql
from base_config import DB_HOST, DB_USER, DB_DATABASE, DB_PASSWORD, DB_PORT


class MysqlHelp():
    """构造
    def __init__(self, host=DB_HOST, user=DB_USER, port=DB_PORT, password=DB_PASSWORD, database=DB_DATABASE):
        self.host = host
        self.user = user
        self.port = port
        self.password = password
        self.db = database
    """
    # 创建连接
    def open_coon(self,host=DB_HOST, user=DB_USER, port=DB_PORT, password=DB_PASSWORD, database=DB_DATABASE):
        self.coon = pymysql.connect(host=host, port=port, user=user, passwd=password, db=database)
        self.cursor = self.coon.cursor(cursor=pymysql.cursors.DictCursor)

    # 关闭连接
    def close(self):
        self.cursor.close()
        self.coon.cursor()

    # 调用语句
    def insert_delete_update(self, sql, params=[]):
        try:
            # self.open_coon()

            self.cursor.execute(sql, params)
            self.coon.commit()

            # self.close()

            return "OK"
        except Exception as erorr:
            return erorr

    # 查询 接收全部的返回结果行

    def select_fetchall(self, sql, params=[]):
        try:
            # self.open_coon()

            self.cursor.execute(sql, params)

            results = self.cursor.fetchall()

            self.coon.commit()

            # self.close()
            return results

        except Exception as erorr:
            return erorr

PostgreSQL，ssh通道操作

#!/usr/bin/env python
# -*- coding: UTF-8 -*-

import psycopg2
import psycopg2.extras
from sshtunnel import SSHTunnelForwarder
import pandas as pd

server = SSHTunnelForwarder(
    # 指定ssh登录的跳转机的address
    ssh_address_or_host=('ip', 22),
    ssh_username='root',
    # 设置密钥
    ssh_pkey='',
    ssh_private_key_password='',

    # 设置数据库服务地址及端口
    remote_bind_address=('***', 5432))
server.start()
conn = psycopg2.connect(database='kong',
                        user='admin',
                        password='****',
                        host='127.0.0.1',
                        port=server.local_bind_port)
# cursor = conn.cursor(cursor=pymysql.cursors.DictCursor)
sql = 'SELECT * FROM "public"."oauth2_tokens" LIMIT 1000 OFFSET 0'
cur = conn.cursor(cursor_factory=psycopg2.extras.RealDictCursor)
cur.execute(sql)
rows = cur.fetchall()


# df = pd.read_sql(sql, conn)
conn.close()
print(rows,type(rows))
server.close()

# conn = psycopg2.connect(database="testdb", user="postgres", password="pass123", host="127.0.0.1", port="5432")

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