Example showing how to add a column in PyTables

addColumn_PyTables.py

from tables import *

# Isolated the copying logic
def append_column(table, group, name, column):
    """Returns a copy of `table` with an empty `column` appended named `name`."""
    
    description = table.description._v_colObjects.copy()
    description[name] = column
    copy = Table(group, table.name+"_copy", description)
    
    # Copy the user attributes
    table.attrs._f_copy(copy)
    
    # Fill the rows of new table with default values
    for i in xrange(table.nrows):
        copy.row.append()
    # Flush the rows to disk
    copy.flush()
    
    # Copy the columns of source table to destination
    for col in descr:
        getattr(copy.cols, col)[:] = getattr(table.cols, col)[:]
    
    # store original name
    #name = table.name
    
    # Remove the original table
    table.remove()
    
    #copy.name = name
    
    return copy
    
# Describe a water class
class Water(IsDescription):
    waterbody_name        = StringCol(16, pos=1)   # 16-character String
    lati        = Int32Col(pos=2)        # integer
    longi       = Int32Col(pos=3)        # integer
    airpressure    = Float32Col(pos=4)    # float  (single-precision)
    temperature = Float64Col(pos=5)      # double (double-precision)

# Open a file in "w"rite mode
fileh = openFile("myadd-column.h5", mode = "w")
# Create a new group
group = fileh.createGroup(fileh.root, "newgroup")

# Create a new table in newgroup group
table = fileh.createTable(group, 'table', Water, "A table", Filters(1))

# Append several rows
table.append([("Atlantic", 10, 0, 10*10, 10**2),
              ("Pacific", 11, -1, 11*11, 11**2),
              ("Atlantic", 12, -2, 12*12, 12**2)])

print "Contents of the original table:", fileh.root.newgroup.table[:]

# Create another table but this time in the root directory
tableroot = fileh.createTable(fileh.root, 'root_table', Water, "A table at root", Filters(1))

# Append data...
tableroot.append([("Mediterranean", 10, 0, 10*10, 10**2),
              ("Mediterranean", 11, -1, 11*11, 11**2),
              ("Adriatic", 12, -2, 12*12, 12**2)])

# close the file
fileh.close()

# Open it again in append mode
fileh = openFile("myadd-column.h5", "a")
group = fileh.root.newgroup
table = group.table

# Get a description of table in dictionary format
descr = table.description._v_colObjects
descr2 = descr.copy()

# Add a column to description
descr2["hot"] = BoolCol(dflt=False)

table2 = append_column(table, group, "hot", BoolCol(dflt=False))

# Move table2 to table
table2.move('/newgroup','table')

# Print the new table
print "Contents of the table with column added:", fileh.root.newgroup.table[:]

# Finally, close the file
fileh.close()