怎么新建MySQL数据库

将datetime64[ns]转为字符串日期

将datetime64[ns]转为字符串日期（“%Y-%m-%d”）最核心的用法是：

pandas.series.dt.strftime('%Y-%m-%d')

如果是DataFrame或Series的index，则转换最核心的用法是：

pandas.DataFrame.index.strftime("%Y-%m-%d")

示例代码

将series转为字符串日期：

import pandas as pd
def convert_datetime(col_series: pd.Series):
    """series datetime64[ns] 转 字符串日期"""
    if col_series.dtype == "datetime64[ns]":
        return col_series.dt.strftime('%Y-%m-%d')
    else:
        return col_series
def main():
    time_series = pd.Series(pd.date_range(start="20200101", periods=20, freq="D"))
    new_time_series = convert_datetime(time_series)
    print(time_series, "\n")
    print(new_time_series)
if __name__ == '__main__':
    main()

使用apply()将整个dataframe的所有datetime64[ns]都转为object类型的日期数据

import pandas as pd
import numpy as np
def convert_datetime(col_series: pd.Series):
    """series datetime64[ns] 转 字符串日期"""
    if col_series.dtype == "datetime64[ns]":
        return col_series.dt.strftime('%Y-%m-%d')
    else:
        return col_series
def main():
    time_df = pd.DataFrame(index=np.arange(0, 20))
    time_df['dt_col'] = pd.date_range(start="20200101", periods=20, freq="D")
    time_df['num_col'] = np.random.random(size=20)
    convert_time_df = time_df.apply(convert_datetime, axis=0)
    print(time_df.dtypes, "\n ==============")
    print(convert_time_df.dtypes)
if __name__ == '__main__':
    main()

python datetime与字符串、时间戳与字符串相互转换

用flask处理前端传过来的时间参数时，有可能是时间，也有可能是字符串，在不需要前端改动的情况下，后端可以自己处理。

情况1：将datetime形式转为需要的字符串

（这样的字符串在写原生sql语句是可以当作实参传递使用）

import datetime
time1 = datetime.datetime.now()
print(type(time1))
print(time1)#假设前端传的形式不符合后端要求
time1 = time1.strftime('%Y-%m-%d %H:%M:%S')#只取年月日，时分秒
print(type(time1))
print(time1)

情况2：将字符串形式的时间转为datetime形式

import time,datetime
str_time = '2020-9-20 21:33:21'
fmt = '%Y-%m-%d %H:%M:%S'
print(str_time)
print(type(str_time))
str_time = datetime.datetime.strptime(str_time, "%Y-%m-%d %H:%M:%S")
print(str_time)
print(type(str_time))

情况3：约定前端传过来datetime形式

形如2020-09-20 21:49:58.986521，我们已经将其处理成了字符串，我们只取前端传过来的年月日，后面时分秒由自己添加，这时我们可以使用原生sql语句进行查询，形如（只需要看懂传字符串能查就行）

point_detect = db.session.execute("select a.id as flag_id,a.patrol_time,b.id as point_id,b.point_number,b.x_coor,b.y_coor from pipe_user_point a left join pipe_point b on a.pipe_point_id = b.id  and a.pipe_user_id = '%s' and a.patrol_time <= '%s' and a.patrol_time >= '%s' and b.is_active = 1" % (patrol_id,start_time,end_time)).fetchall()

import time,datetime
start_time = datetime.datetime.now()
print(type(start_time))
print(start_time)#假设前端传的形式不符合后端要求
start_time = start_time.strftime('%Y-%m-%d')#只取年月日 时分秒由自己添加
print(type(start_time))
print(start_time)
start_time = start_time + ' 00:00:00'
print(type(start_time))
print(start_time)
end_time = datetime.datetime.now().strftime('%Y-%m-%d %H:%M:%S')
print(type(end_time))
print(end_time)

情况4：对datetime形式的时间进行减操作

其中end_time会减去一天

import time,datetime
start_time = datetime.datetime.now()
print(type(start_time))
print(start_time)
end_time = datetime.datetime.now()
print(type(end_time))
print(end_time)
time = start_time - datetime.timedelta(days=1)#取一天之前
print(type(time))
print(time)
time = time.strftime('%Y-%m-%d %H:%M:%S')
print(type(time))
print(time)

21-7-7更新

情况5：将前端毫秒时间戳转为年月日时分秒

def time_change_str(int_millisecond_time_stamp):
    dateArray = datetime.datetime.fromtimestamp(int_millisecond_time_stamp / 1000)
    otherStyleTime = dateArray.strftime("%Y-%m-%d %H:%M:%S")
    return otherStyleTime
 
#flask中的model.query.filter(model.report_time >= time1)可行