Python常见用法
Python常见用法一、Pandas-DataFrame数据结构
DataFrame 是一个表格型的数据结构,它含有一组有序的列,每列可以是不同的值类型(数值、字符串、布尔型值)。DataFrame 既有行索引也有列索引,它可以被看做由 Series 组成的字典(共同用一个索引)。
1.1 创建1.1.1 使用列表创建data = [["Google", 10], ["Runoob", 12], ["Wiki", 13]] df = pd.DataFrame(data, columns=["Site", "Age"]) print(df) 复制代码1.1.2 使用ndarrays创建data = {"Site":["Google", "Runoob", "Wiki"], "Age":[10, 12, 13]} df = pd.DataFrame(data) print (df) 复制代码1.1.3 使用字典创建data = [{"a": 1, "b": 2}, {"a": 5, "b": 10, "c": 20}] df = pd.DataFrame(data) print(df) 复制代码1.2 读取1.2.1 df.loc[idx]data = { "calories": [420, 380, 390], "duration": [50, 40, 45] } # 数据载入到 DataFrame 对象 df = pd.DataFrame(data) # 返回第一行 print(df.loc[0]) # 返回第二行 print(df.loc[1]) # 返回第一行和第二行 print(df.loc[[0, 1]]) 复制代码data = { "calories": [420, 380, 390], "duration": [50, 40, 45] } df = pd.DataFrame(data, index = ["day1", "day2", "day3"]) # 指定索引 print(df.loc["day2"]) 复制代码1.2.2 df.iterrows()# 将DataFrame迭代为(index, Series)对 for index, row in df.iterrows(): score = row["score"] name = row["name"] 复制代码1.2.3 df.iteritems()# 将DataFrame迭代为(列名, Series)对 for index, row in df.iteritems(): score = row["score"] name = row["name"] 复制代码二、CSV操作2.1 读取文件df = pd.read_csv("site.csv") # to_string() 用于返回 DataFrame 类型的数据,如果不使用该函数,则输出结果为数据的前面 5 行和末尾 5 行,中间部分以 ... 代替 print(df.to_string()) 复制代码2.1 写入文件import pandas as pd # 三个字段 name, site, age nme = ["Google", "Runoob", "Taobao", "Wiki"] st = ["www.google.com", "www.runoob.com", "www.taobao.com", "www.wikipedia.org"] ag = [90, 40, 80, 98] # 字典 dict = {"name": nme, "site": st, "age": ag} df = pd.DataFrame(dict) # 保存 dataframe df.to_csv("site.csv") 复制代码import csv writer = csv.writer(open("relax_label_results.csv", "w"), delimiter=" ") writer.writerow(["songid", "relax_prob", "relax_pred"]) writer.writerow(["123", "abc", "dgf"]) 复制代码三、字典操作3.1 读取字典# 遍历key和value for key, value in dict.items(): # keys()遍历是无序的 for key in dict.keys(): # 利用sorted()使keys有序遍历 for key in sorted(dict.keys()): # 遍历value for value in dict.values(): 复制代码3.2 写入字典dict["a"] = 1 # 直接赋值 复制代码3.3 移除key# 删除key值为"a"的元素,并赋值给变量value,若key不存在,则报错 value = d.pop("a") # 如果key不存在,则可以设置返回值 value = d.pop("a","404") 复制代码四、conda创建虚拟环境4.1 创建新环境conda create -n my_py_env(环境名称) python=3.6 复制代码4.2 删除环境conda remove -n my_py_env --all 复制代码4.3 使用环境# 触发进入 conda activate my_py_env # 退出环境 conda deactivate 复制代码五、APScheduler5.1 安装pip install apscheduler 复制代码5.2 简单示例from apscheduler.schedulers.blocking import BlockingScheduler import time # 实例化一个调度器 scheduler = BlockingScheduler() def job1(): print("start") # 添加任务并设置触发方式为3s一次 scheduler.add_job(job1, "interval", seconds=3) # 开始运行调度器 scheduler.start() 复制代码5.3 三种trigger方式5.3.1 date
只在某个时间点执行一次run_date(datetime|str)scheduler.add_job(my_job, "date", run_date=date(2017, 9, 8), args=[]) scheduler.add_job(my_job, "date", run_date=datetime(2017, 9, 8, 21, 30, 5), args=[]) scheduler.add_job(my_job, "date", run_date="2017-9-08 21:30:05", args=[]) 复制代码5.3.2 interval
每隔一段时间执行一次weeks=0 | days=0 | hours=0 | minutes=0 | seconds=0, start_date=None, end_date=None, timezone=Nonescheduler.add_job(my_job, "interval", hours=2) scheduler.add_job(my_job, "interval", hours=2, start_date="2017-9-8 21:30:00", end_date="2018-06-15 21:30:00) @scheduler.scheduled_job("interval", id="my_job_id", hours=2) def my_job(): print("Hello World") 复制代码5.3.3 cron
使用同linux下crontab的方式(year=None, month=None, day=None, week=None, day_of_week=None, hour=None, minute=None, second=None, start_date=None, end_date=None, timezone=None)sched.add_job(my_job, "cron", hour=3, minute=30) sched.add_job(my_job, "cron", hour=5, minute=30, end_date="2017-10-30") @sched.scheduled_job("cron", id="my_job_id", day="last sun") def some_decorated_task(): print("I am printed at 00:00:00 on the last Sunday of every month!")