Running Python¶

The normal way to run Python is simply to enter

py xxx

where xxx is the root name of a parameter file. (The full name xxx.pf can also be entered).

However Python features a number of command line options which can be used to modify it’s operation. These include the following:

`-h`	Causes Python to print out a brief help message and quit. The help message principally describes the command line options

-i (or –dry-run): Causes Python to read and verify the inputs, writing a clean version of the input file xxx.pf to the output file xxx.out.pf, and then stop. This option is useful for setting up a proper .pf file. (Often one will want to copy xxx.out.pf back to xxx.pf before proceeding.

`-t time_max`	Limits a run of python to approximately time_max in sec. This switch is used in situations where one would like to check whether the routine is operating properly be continuing, or where one needs to checkpoint the program after a certain period of time (due for example to time limits placed on jobs in a Beowulf cluster). The time is checked at the end of ionization and spectral cycles, immediately after saving the binary files that describe a model, and so one needs to leave a cushion between time_max and the maximum time one wants the program to run
`-r`	Restarts a run that has been interrupted or halted, by reading a the `xxx.windsave` and `xxx.specsave` file (if it exists).
`-v n`	Changes the amount of information printed to the screen by Python during a run. The default is 4. Larger numbers increase this. Smaller numbers decrease it. The log files are not affected.
`--rseed`	Causes Python to use a random number seed that is time-based, rather than fixed. In most cases, a fixed seed is preferred so that problems can be replicated, but if is repeating the same calculation multiple times, then one may want a random seed.
`--version`	Causes Python to print out the version number and commit hash (and whether uncommitted files exist, and then stop.
`-p n_steps`	Changes the number of photons generated during ionization cycles so that the number increases logarithmically to the maximum value. The number `n_steps` is optional, and specifies the number of decades over which the increase takes place. Todo NEED TO VERIFY THIS

Special switches¶

Python has a number of other switches that are not intended for the general user, but which may be useful in certain special cases. These include:

`-d`	Enables a variety of specialized diagnostic inputs which have been implemented to help with solving various problems, and were regarded (by someone) as useful enough to maintain in the program. The user is then queried regarding which of these diagnostics to enable for a specific run. These diagnostic queries all start with @ (and can co-exist in the `.pf` file, with normal commands.
`-e n`	Where `n` is a number, changes the number of errors of a specific type that are allowed to occur before the program gives up. For a variety of reasons, errors are expected during Python runs. Most of these errors are harmless in the sense that they occur rarely. But if an error occurs too often, something is seriously and so Python halts at that point. The default is \(10^{5}\) (per thread).

-e write n: Changes the number of times an error message of a specific type is written to a diagnostic file. When errors occur, a line describing the error is written to the diagnostic file the first n times the error occurs. After that statistics are maintained as to the number of times the error occurred, but it is not printed to the diagnostic file. The default is 100 (per thread)