学习笔记：python3，代码片段（2017）

#输出PI
from math import pi
print(pi)

3.141592653589793

from datetime import datetime
t = 0
print(datetime.fromtimestamp(t))

1970-01-01 00:00:00

#当前时间
import time
print(time.time())

1490681347.365674

from datetime import datetime
t = time.time()
print(t)
print(datetime.fromtimestamp(t))

1490681423.5541148
2017-03-28 06:10:23.554114

#将一个list列表对象，进行了json格式的编码转换
import json
l = [‘iplaypython‘,[1,2,3], {‘name‘:‘xiaoming‘}]
encoded_json = json.dumps(l) #将列表，进行json格式化编码
print (repr(l))
print (encoded_json)

decode_json = json.loads(encoded_json)
print (type(decode_json))
print (type(encoded_json))

#连接数据库
import pymysql
print(pymysql.VERSION)
conn = pymysql.Connect(host=‘localhost‘,user=‘root‘,passwd=‘qin‘,db=‘person‘,port=3306,charset=‘utf8‘)
cur = conn.cursor()
cur.execute("select * from dream")
print (cur.rowcount)

#数据库查询结果，用json返回
import json
import pymysql
conn = pymysql.Connect(host=‘localhost‘,user=‘root‘,passwd=‘python‘,db=‘zzdb‘,port=3306,charset=‘utf8‘)
cur = conn.cursor()
cur.execute("select * from users")
print (‘共有‘,cur.rowcount,‘条数据‘)

users=[]
data = {}
results = cur.fetchall()
for r in results:
    print(r[0],end=‘ ‘)
    print(r[1],end=‘ ‘)
    print(r[2],end=‘ ‘)
    print("---")
    person = {}
    person[‘id‘] = r[0]
    person[‘name‘] = r[1]
    person[‘age‘] = r[2]
    users.append(person)
cur.close()
conn.close()
data[‘code‘] = 0
data[‘msg‘] = ‘成功‘
data[‘users‘] = users
jsonStr = json.dumps(data)
print(jsonStr)

#读文件
f = open("c:\\1.txt","r")
lines = f.readlines()
for line in lines:
   print( line)

#写文件
f = open("c:\\1.txt","r+")
f.write("123")#写入字符串

#每运行一次，追加一下更改时间
import time
from datetime import datetime
try:
    f = open(‘1.txt‘, ‘r+‘)
    sss = f.read()
    print(sss)
    t2 = datetime.fromtimestamp(float(time.time()))
    f.write(‘\n‘+str(t2))
finally:
    if f:
        f.close()

#把图片缩小到二分之一
from PIL import Image, ImageFilter
im = Image.open(‘1.jpg‘)
w, h = im.size
print(‘原图片尺寸: %sx%s‘ % (w, h))
# 缩放到50%:
im.thumbnail((w//2, h//2))
# 把缩放后的图像用jpeg格式保存:
im.save(‘2.jpg‘, ‘jpeg‘)
#要详细了解PIL的强大功能，请请参考Pillow官方文档： https://pillow.readthedocs.org/

#写EXCEL文件
# -*- coding: utf-8 -*-
import xlwt

book = xlwt.Workbook(encoding = "utf-8", style_compression = 0)#创建一个Wordbook对象，相当于创建了一个Excel文件
sheet = book.add_sheet("sheet1", cell_overwrite_ok = True)#创建一个sheet对象，一个sheet对象对应Excel文件中的一张表格

#向表sheet1中添加数据
#sheet.write(0, 0, "1行1列")
#sheet.write(1, 0, "2行1列")
#sheet.write(0, 1, "1行2列")
#sheet.write(1, 1, "2行2列")
for i in range(0,30):
    sheet.write(i,0,i)
    sheet.write(i,1,i*2)
    sheet.write(i,2,i*3)
#最后，将以上操作保存到指定的Excel文件中
book.save("zz.xls")

#读EXCEL文件的内容
import xlrd
xls_file = "zz.xls"
book = xlrd.open_workbook(xls_file)#打开指定文件
sheet1 = book.sheet_by_index(0)# 通过sheet索引获得sheet对象
# 获得行数和列数
nrows = sheet1.nrows# 总行数
ncols = sheet1.ncols#总列数
# 遍历打印表中的内容
for i in range(nrows):
    for j in range(ncols):
        cell_value = sheet1.cell_value(i, j)
        print(cell_value, end = "\t")
    print("")

# -*- coding: utf-8 -*-
import requests
import urllib

# 榜单歌曲批量下载
#http://music.163.com/discover/toplist?id=3779629    id来自于 http://music.163.com/ 的“云音乐新歌榜”
r = requests.get(‘http://music.163.com/api/playlist/detail?id=3779629‘)
arr = r.json()[‘result‘][‘tracks‘]    # 共有100首歌

for i in range(10,20):    # 输入要下载音乐的数量，1到100。
    name = str(i+1) + ‘ ‘ + arr[i][‘name‘] + ‘.mp3‘
    link = arr[i][‘mp3Url‘]
    urllib.request.urlretrieve(link, ‘网易云音乐\\‘ + name)    # 提前要创建文件夹
    print(name + ‘ 下载完成‘)