[Python] How do I incrementally add rows in Pandas Dataframe?

I am calculating the open-high-low-close (OHLC) of data for a duration of each 15 mins from 9:15 to 15:30 and want to store the OHLC values in a dataframe in each new row.

ohlc = pd.DataFrame(columns=('Open','High','Low','Close'))
for row in ohlc:
ohlc.loc[10] = pd.DataFrame([[candle_open_price,candle_high_price,candle_low_price,candle_close_price]])


But I am not able to do say getting an error of:

ValueError: cannot set a row with mismatched columns


Just I want to incrementally store the OHLC data of each 15-minute duration which I have calculated & put in rows of the new ohlc dataframe


EDIT

import numpy as np
import pandas as pd
import datetime as dt
import matplotlib as plt
import dateutil.parser

tradedata = pd.read_csv('ICICIBANK_TradeData.csv', index_col=False,
names=['Datetime','Price'],
header=0)
tradedata['Datetime'] = pd.to_datetime(tradedata['Datetime'])

first_trd_time = tradedata['Datetime'][0]
last_time = dateutil.parser.parse('2016-01-01 15:30:00.000000')

candle_time = 15;
candle_number = 0

while(first_trd_time < last_time):
candledata = tradedata[(tradedata['Datetime']>first_trd_time) & (tradedata['Datetime']<first_trd_time+dt.timedelta(minutes=candle_time))]
first_trd_time = first_trd_time+dt.timedelta(minutes=candle_time)

candle_open_price = candledata.iloc[0]['Price']
candle_open_time = candledata.iloc[0]['Datetime']
candle_close_price = candledata.iloc[-1]['Price']
candle_close_time = candledata.iloc[-1]['Datetime']
candle_high_price = candledata.loc[candledata['Price'].idxmax()]['Price']
candle_high_time = candledata.loc[candledata['Price'].idxmax()]['Datetime']
candle_low_price = candledata.loc[candledata['Price'].idxmin()]['Price']
candle_low_time = candledata.loc[candledata['Price'].idxmin()]['Datetime']

ohlc = pd.DataFrame(columns=('Open','High','Low','Close'))
ohlc_data = pd.DataFrame()

if(candle_number == 0):
ohlc = pd.DataFrame(np.array([[0, 0, 0, 0]]), columns=['Open', 'High', 'Low', 'Close']).append(ohlc, ignore_index=True)
candle_number = candle_number + 1
print "Zeroth Candle"
else:
ohlc.ix[candle_number] = (candle_open_price,candle_open_price,candle_open_price,candle_open_price)
print "else part with incermenting candle_number"
candle_number = candle_number + 1

print "first_trd_time"
print first_trd_time
print candle_number

print "Success!"


This is my code error is

ValueError: cannot set by positional indexing with enlargement




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