Converting strings to a lower case in pandas [duplicate]
I think you need assign output back, better is omit apply if works only with column url:
df = pd.DataFrame({'url': ['www.CNN.com', 'www.Nbc.com', 'www.BBc.com', 'www.fOX.com'], 'var1': ['XSD', 'wer', 'xyz', 'zyx']})print (df) url var10 www.CNN.com XSD1 www.Nbc.com wer2 www.BBc.com xyz3 www.fOX.com zyx#if types of column is str, astype is not necessarydf.url = df.url.astype(str).str.lower()print (df) url var10 www.cnn.com XSD1 www.nbc.com wer2 www.bbc.com xyz3 www.fox.com zyxBut if need convert all columns of df to lowercase strings:
df = df.astype(str).apply(lambda x: x.str.lower())print (df) url var10 www.cnn.com xsd1 www.nbc.com wer2 www.bbc.com xyz3 www.fox.com zyx