创建DataFrame or 插入行（DataFrame.append / DateFrame.loc）

对比了readline速度，
使用list.append并一次合并DataFrame，
使用逐行创建DataFrame，再用DataFrame.append合并，
使用DataFrame.loc[] = []的方式逐行插入数据。

为DataFrame插入数据是非常不建议的选择，
应该直接用list装入所有数据，最后一次性合成DataFrame。
（文件大小：6200 kb，43000 行）

import pandas as pd
from datetime import *


def test(path):
	start = datetime.now()
	with open(path) as f:
		all = pd.DataFrame()
		while True:
			i_line = f.readline()
			if i_line == "":
				break
			if i_line.find("Date") == -1:
				new = pd.DataFrame({"Date":i_line.split(",")[0],"value":i_line.split(",")[6]},index=["0"])
				all = all.append(new, ignore_index=True)
	end = datetime.now()
	print(end-start)
	return all

def test_loc(path):
	start = datetime.now()
	with open(path) as f:
		all_loc = pd.DataFrame({"Date":[],"value":[]},index=[])
		n=0
		while True:
			i_line = f.readline()
			if i_line == "":
				break
			if i_line.find("Date") == -1:
				all_loc.loc[n] = [i_line.split(",")[0], i_line.split(",")[6]]
				n+=1
	end = datetime.now()
	print(end-start)
	return all_loc

def test_readline(path):
	start = datetime.now()
	with open(path) as f:
		while True:
			i_line = f.readline()
			if i_line == "":
				break
			if i_line.find("Date") == -1:
				pass
	end = datetime.now()
	print(end-start)

def test_list(path):
	start = datetime.now()
	with open(path) as f:
		list_date = []
		list_value = []
		while True:
			i_line = f.readline()
			if i_line == "":
				break
			if i_line.find("Date") == -1:
				list_date.append(i_line.split(",")[0])
				list_value.append(i_line.split(",")[6])
	all_list = pd.DataFrame({"Datetime":list_date, "value":list_value})
	end = datetime.now()
	print(end-start)
	return all_list

test_readline(path)
df_list = test_list(path)
df = test(path)
df_loc = test_loc(path)

# 0.006s
# 0.153s
# 1M0.52S
# 2M40S