# pythoncall¶

author: | Pauli Virtanen <pav@iki.fi> |
---|---|

version: | 0.3.1 |

Python embedded inside Matlab.

Conversion of basic types + numeric array types between Python and Matlab is provided.

Note

This is still in relatively early stages of work, but I have used it for example for loading HDF5 files using PyTables. (Since frankly, Matlab’s HDF5 support has been quite inadequate.)

Also, this code has been tested only on Linux platforms.

## Usage¶

Evaluate python string:

pythoncall('eval', command)

`command`

is a string containing the Python program to run. It is run in the __main__ module.Get variable values from the Python space:

[value1, value2, ...] = pythoncall('get', varname1, varname2, ...)

This gets variables from the top-level of __main__ module.

Set variable values to the Python space:

pythoncall('set', varname1, value1, varname2, value2, ...)

This sets variables to the top-level of __main__ module.

## Compilation (important!)¶

Note that Matlab apparently `dlopens`

its extensions with RTLD_GLOBAL
disabled. This means that if you load the Python interpreter inside
Matlab without extra tricks, any extensions modules loaded by Python
will not be able to see Python symbols. Which means that they do not
work, which is especially annoying since you surely would like to use
for example numpy.

To work around this nasty limitation, `pythoncall.c`

has an equally nasty
hack: it explicitly loads symbols in the Python library to its own
“namespace”, by `dlopening`

the Python library file. To do this,
it needs to know the location of Python’s `libpython2.X.so`

file.
Have a look at the `Makefile`

and fix the location of `LIBPYTHON`

to match your version of Python.

While you’re at it, also change `-DNUMPY`

to `-DNUMARRAY`

or
`-DNUMERIC`

if you use one of the earlier array libraries of Python.

## Type conversion¶

The whole point of having Python inside Matlab is to have easy
conversion of variables. In `pythoncall`

this goes as follows:

From | To |
---|---|

Python int | Matlab 1x1 int32 |

Python float | Matlab 1x1 double |

Python complex | Matlab 1x1 double complex |

Python bool | Matlab 1x1 logical |

Python dict | Matlab 1x1 struct array. Field names: repr(key) |

Python object array | Matlab cell array |

Python array | Matlab array |

Python sequence | Matlab 1xN cell array |

Python None | Matlab empty cell array |

Python other | Matlab empty cell array + warning |

Matlab cell array | Python list if one-dim, otherwise python object array |

Matlab char array | Python string if one-dim, otherwise python numeric array |

Matlab struct array | Python dict. If 1x1, values are converted directly. If not scalar, values are python arrays/obj-arrays, same size as the struct. |

Matlab array | Python array |

Matlab other | Python None + warning |

## Files¶

- Development version on github
`pythoncall.c`

: Source code`Makefile`

: Makefile`h5load.m`

: Matlab function using`pythoncall`

to interface with Pytables to load HDF5 files (better than Matlab’s built-in functionality, as of R2006a)