NoSuchNodeError when determine tables in file

Question

I use PyTables, I want to check whether a table has been created or not, if not, then create it.

I use the following code:

if handle.__contains__(handle.root.grades)==False:
    handle.create_table('/', 'grades', grades)

while when there is no such table named "grades", the program report error:"NoSuchNodeError: group / does not have a child named grades"

once there is a table named "grades", the following

handle.__contains__(handle.root.grades)

returns True.

How should I determine whether there is certain table?

Answer 1

I use the following expression to deal with the problem.

import tables as tb
try:
   handle.__contains__(handle.root.grades)
   print('contains grades')
except tb.NoSuchNodeError:
   print('there is no grades, will create it')
   handle.create_table('/', 'grades', grades)

and in Pytables, the expression for file.contains is

def __contains__(self, path):

    try:
        self.get_node(path)
    except NoSuchNodeError:
        return False
    else:
        return True

so, does pytables have some problems? or I don't import tables correctly?