python pandas select test

# 配列計算
import pandas as pd
import numpy as np
import datetime as dt

# グラフ描画
import matplotlib as mpl
import matplotlib.pyplot as plt

df = pd.read_csv('data/1234_all.csv',
header=0,
encoding="shift-jis")

# 型を指定
df['日付'] = df['日付'].astype(np.datetime64)
df['高値'] = df['高値'].astype(np.float32)
df['安値'] = df['安値'].astype(np.float32)
df['終値'] = df['終値'].astype(np.float32)


start = '20120309'
today = '20120313'
days = 10
approach_days = 50

df = df[df['日付'] < dt.datetime(int(today[0:4]), int(today[4:6]), int(today[6:8]))]
df = df[-approach_days:]