How can I use a loop to apply a function to a list of csv files? - pandas

Question

I'm trying to loop through all files in a directory and add "indicator" data to them. I had the code working where I could select 1 file and do this, but now am trying to make it work on all files. The problem is when I make the loop it says
ValueError: Invalid file path or buffer object type: <class 'list'>
The goal would be for each loop to read another file from list, make changes, and save file back to folder with changes.
Here is complete code w/o imports. I copied 1 of the "file_path"s from the list and put in comment at bottom.
### open dialog to select file
#file_path = filedialog.askopenfilename()
###create list from dir
listdrs = os.listdir('c:/Users/17409/AppData/Local/Programs/Python/Python38/Indicators/Sentdex Tutorial/stock_dfs/')
###append full path to list
string = 'c:/Users/17409/AppData/Local/Programs/Python/Python38/Indicators/Sentdex Tutorial/stock_dfs/'
listdrs_path = [ string + x for x in listdrs]
print (listdrs_path)
###start loop, for each "file" in listdrs run the 2 functions below and overwrite saved csv.
for file in listdrs_path:
file_path = listdrs_path
data = pd.read_csv(file_path, index_col=0)
########################################
####function 1
def get_price_hist(ticker):
# Put stock price data in dataframe
data = pd.read_csv(file_path)
#listdr = os.listdir('Users\17409\AppData\Local\Programs\Python\Python38\Indicators\Sentdex Tutorial\stock_dfs')
print(listdr)
# Convert date to timestamp and make index
data.index = data["Date"].apply(lambda x: pd.Timestamp(x))
data.drop("Date", axis=1, inplace=True)
return data
df = data
##print(data)
######Indicator data#####################
def get_indicators(data):
# Get MACD
data["macd"], data["macd_signal"], data["macd_hist"] = talib.MACD(data['Close'])
# Get MA10 and MA30
data["ma10"] = talib.MA(data["Close"], timeperiod=10)
data["ma30"] = talib.MA(data["Close"], timeperiod=30)
# Get RSI
data["rsi"] = talib.RSI(data["Close"])
return data
#####end functions#######
data2 = get_indicators(data)
print(data2)
data2.to_csv(file_path)
###################################################
#here is an example of what path from list looks like
#'c:/Users/17409/AppData/Local/Programs/Python/Python38/Indicators/Sentdex Tutorial/stock_dfs/A.csv'

Answer 1

The problem is in line number 13 and 14. Your filename is in variable file but you are using file_path which you've assigned the file list. Because of this you are getting ValueError. Try this:
### open dialog to select file
#file_path = filedialog.askopenfilename()
###create list from dir
listdrs = os.listdir('c:/Users/17409/AppData/Local/Programs/Python/Python38/Indicators/Sentdex Tutorial/stock_dfs/')
###append full path to list
string = 'c:/Users/17409/AppData/Local/Programs/Python/Python38/Indicators/Sentdex Tutorial/stock_dfs/'
listdrs_path = [ string + x for x in listdrs]
print (listdrs_path)
###start loop, for each "file" in listdrs run the 2 functions below and overwrite saved csv.
for file_path in listdrs_path:
data = pd.read_csv(file_path, index_col=0)
########################################
####function 1
def get_price_hist(ticker):
# Put stock price data in dataframe
data = pd.read_csv(file_path)
#listdr = os.listdir('Users\17409\AppData\Local\Programs\Python\Python38\Indicators\Sentdex Tutorial\stock_dfs')
print(listdr)
# Convert date to timestamp and make index
data.index = data["Date"].apply(lambda x: pd.Timestamp(x))
data.drop("Date", axis=1, inplace=True)
return data
df = data
##print(data)
######Indicator data#####################
def get_indicators(data):
# Get MACD
data["macd"], data["macd_signal"], data["macd_hist"] = talib.MACD(data['Close'])
# Get MA10 and MA30
data["ma10"] = talib.MA(data["Close"], timeperiod=10)
data["ma30"] = talib.MA(data["Close"], timeperiod=30)
# Get RSI
data["rsi"] = talib.RSI(data["Close"])
return data
#####end functions#######
data2 = get_indicators(data)
print(data2)
data2.to_csv(file_path)
Let me know if it helps.