如何在Python建立時間序列(Python Generate Datetime Series)

在寫爬蟲程式時，常會需要利用日期序列，來抓每一日的網路資料。

這時候，知道如何產生時間序列就很重要!


1.  datetime：

import datetime

begin = datetime.datetime(2019, 1, 1)
end = datetime.datetime(2019, 1, 3)
step = datetime.timedelta(days=1)

DatePeriod = []

while begin <= end:
    DatePeriod.append(begin.strftime('%Y%m%d'))
    begin += step

print(DatePeriod)
print(type(DatePeriod))

for Day in DatePeriod:
    print(Day)
print(type(Day))

2. pandas：

import pandas as pd
import numpy as np

# 設定起訖日期DatePeriod = pd.date_range("2019/1/1", "2019/1/3", freq='D')
# 將DatePeriod格式化成像要的格式，以及最重要的把時間由index改為string

dp1 = DatePeriod.strftime('%Y%m%d')

print(DatePeriod)
print(type(dp1))
for Day in dp1:
    print(Day)
print(type(Day))

PS：
strftime這函式很重要，可以把時間序列從index變為string!

date = dataframe.index #date is the datetime index
date = dates.strftime('%Y-%m-%d') #this will return you a numpy array, element is string.
dstr = date.tolist() #this will make you numpy array into a list

PPS:

freq 的部分除了 D 也可以換成其他參數，例如 H 是小時、M 是月份，或參考下表：

Alias	Description
B	business day frequency
C	custom business day frequency (experimental)
D	calendar day frequency
W	weekly frequency
M	month end frequency
SM	semi-month end frequency (15th and end of month)
BM	business month end frequency
CBM	custom business month end frequency
MS	month start frequency
SMS	semi-month start frequency (1st and 15th)
BMS	business month start frequency
CBMS	custom business month start frequency
Q	quarter end frequency
BQ	business quarter endfrequency
QS	quarter start frequency
BQS	business quarter start frequency
A	year end frequency
BA	business year end frequency
AS	year start frequency
BAS	business year start frequency
BH	business hour frequency
H	hourly frequency
T, min	minutely frequency
S	secondly frequency
L, ms	milliseconds
U, us	microseconds
N	nanoseconds

參考來源：

Python Generate Datetime Series

https://coder.tw/?p=7650

python+pandas+時間、日期以及時間序列處理方法

https://www.itread01.com/article/1531186144.html

https://stackoverflow.com/questions/30132282/datetime-to-string-with-series-in-python-pandas

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http://www.coco-in.net/forum.php?mod=viewthread&tid=38351&page=2
也可以參考別人寫的

以下說明日期字串的產生方式與迴圈 以下是粗略的代碼，請自行調整成你所要的 假設先指定開始與結束日期字串： 我習慣用西元，在後面會轉成民國年 date_s = '20150801' date_e = '20150831' 複製代碼 轉換成日期型別： from datetime import date, timedelta from time import sleep date_s = date(int(date_start[:4]), int(date_start[4:6]), int(date_start[6:8])) date_e = date(int(date_end[:4]), int(date_end[4:6]), int(date_end[6:8])) 複製代碼 開始日期與結束日期間的迴圈： while date_s <= date_e:     yyyy = date_s.strftime('%Y')     mm = date_s.strftime('%m')     dd = date_s.strftime('%d')     # 產生民國“年/月/日”字串     twymd = '{}/{}/{}'.format(int(yyyy) - 1911, mm, dd)     data = {'download': 'csv', 'qdate': twymd, 'selectType': 'ALLBUT0999'}     # 下載資料，這裡省略。     # 暫停一秒     sleep(1)     # 把日期加一日        date_s = date_s + timedelta(days=1) 複製代碼