3.2.1.0 table.open

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table.open - Function

3.2.1 open an existing table

Description

Opens a disk file containing an existing CASA Table.

Most of the time you just need to specify the tablename and perhaps nomodify.

A table can be shared by multiple processes by using the appropriate locking options. The possible options are:
- auto: let the system take care of locking. At regular time intervals these autolocks are released to give other processes the opportunity to access the table.
- autonoread: as auto, but no read locking is needed. This must be used with care, because it means that reading can be done while the table tool is not synchronized with the table file (as is normally done when a lock is acquired). The function resync can be used to explicitly synchronize the table tool
- user: the user takes care by explicit calls to lock and unlock
- usernoread: as user and the no readlocking behaviour of autonoread.
- permanent: use a permanent lock; the constructor fails when the table is already in use in another process
- permanentwait: as above, but wait until the other process releases its lock
- default: this is the default option. If the given table is already open, the locking option in use is not changed. Otherwise it reverts to auto.
When auto locking is used, it is possible to give a record containing the fields option, interval, and/or maxwait. In this way advanced users have full control over the locking options. In practice this is hardly ever needed.

Arguments


Inputs
tablename
	allowed:	string
	Default:
lockoptions	locking dictionary to be used : dict keys are ’option’, ’interval’, ’maxwait’
	allowed:	record
	Default:
nomodify
	allowed:	bool
	Default:	true

Returns
bool

Example

  # First let’s make a table for testing
  def maketesttable():
      # Get path to CASA home directory by stipping name from ’$CASAPATH’
      pathname=os.environ.get("CASAPATH").split()[0]
      # This is where the 3C273XC1.fits data should be
      fitsdata=pathname+"/data/demo/3C273XC1.fits"
      # Remove old table if present
      !rm -rf 3C273XC1.MS
      ms.fromfits("3C273XC1.MS",fitsdata)
      ms.close()

  maketesttable()
  tb.open("3C273XC1.MS")
  tb.browse()
  tb.close()

The first line opens an existing table 3C273XC1.MS, the second browses
it using the browse function.

  tb.open("3C273XC1.MS", nomodify=False, lockoptions={’option’:’user’})
  tb.lock();
  tb.addrows();
  tb.unlock();

In this example explicit user locking is used. The function lock
is needed to acquire a (write) lock before the addrows is done.
Thereafter the lock is released to give other processes the chance
to operate on the table.
\\Note that releasing a lock implies flushing the table, so doing
that very often can be quite expensive.

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