import pandas as pd
import time

def timmer(func):
    def warpper(*args,**kwargs):
        start_time = time.time()
        func()
        stop_time = time.time()
        print ("the func run time is %s"%(stop_time - start_time))
    return warpper

def add(num):
    return num+2

df = pd.DataFrame(
    columns=['a','b','c','d','e','f'],
    index=['date','value'],
    data=[['1/1/13 0:00','1/1/13 1:00','1/1/13 2:00','1/1/13 3:00','1/1/13 4:00','1/1/13 5:00'],[0.1,0.2,3,4,5,0.6]]
).T
df

pd.__version__

@timmer
def test_1():
    for x in range(1000):
        df['date'] = df['date'].apply(lambda x:'1/1/13 1:00')     
        df['date'] = pd.to_datetime(df['date'])                 
test_1()

@timmer
def test_2():
    for x in range(1000):
        df['date'] = df['date'].apply(lambda x:'1/1/13 1:00')
        df['date'] = pd.to_datetime(df['date'], format='%d/%m/%y %H:%M')
test_2()

@timmer
def test_3():
    for x in range(1000):
        for x in df.index:                  
             df.loc[x, 'value'] = df.loc[x, 'value'] + 0.002
@timmer
def test_4():
    for x in range(1000):
        for index,row in df.iterrows():                             
            row['value'] = row['value'] + 0.002
@timmer
def test_5():
    for x in range(1000):
        for index,date,value in df.itertuples():                       
            value = value + 0.002
@timmer
def test_6():
    for x in range(1000):
        df['value'] = df['value'].apply(add)    
@timmer
def test_7():
    for x in range(1000):
        df['value'] = df['value'].apply(lambda x:x+2)        
@timmer
def test_8():
    for x in range(1000):
        df['value']+=0.002      
        
test_3()
test_4()
test_5()
test_6()
test_7()
test_8()