how to update column in data frame based on condition
You access string functions with .str. This should work:

df.loc[df.Lvalue.str.istitle(), 'IsLCap'] = 1

Update
To check the length of the strings in the column you can use the string method .str.len:

df.loc[df.Lvalue.str.len() &lt; 3, 'less_than_three'] = 1

Pandas Series string methods