code: def is_erc20(self):
          
          full_names = [f.full_name for f in self.functions]
          return 'transfer(address,uint256)' in full_names and\
                 'transferFrom(address,address,uint256)' in full_names and\
                 'approve(address,uint256)' in full_names
docs: Check if the contract is an erc20 token
  
              Note: it does not check for correct return values
          Returns:
              bool