Mlabwrap is a highlevel pythontomatlab bridge. This wikipage is currently intended for developers and not for users. Please have a look at the sourceforge page to get a quick overview.
Infrastructure
code is here
use
svn co http://svn.scipy.org/svn/scikits/trunk/mlabwrap
to get the development versionwebpage is ??? (actually right [MlabWrap here] in all likelihood; this developer info will be moved)
 lowvolume user mailing list specific to mlabwrap seems desirable (so keep
mlabwrap@sourceforge.net for the time being)
developer discussions on [projects.scipy.org/mailman/listinfo/scipydev scipydev] list; make sure subject: contains 'mlabwrap'
Design Goals
Mlabwrap strives to
 be painless to install and use (and upgrade)
 (where possible) come close to giving the user the impression to be using a python library rather than calling into a different language
meet the needs of NIPY
One reason for 2. (rather than say striving to emulate the look and feel of matlab as closely as possible) is that it should make it easier to gradually replace legacy matlab code with python code and for python (only) programmers to maintain and understand code that uses mlabwrap to leverage an existing matlab code base. The downside is that there is enough semantic difference between matlab and python (see below) to make this goal fully attainable  tradeoffs will have to be made.
I think it's therefore important that these tradeoffs are informed by actual usage patterns, which is why 3. is likely to be vital for arriving at a good design; deriving things from first principles is unlikely to be an adequate substitute.
Principles
 Design approach: First consider the most common usecases and how they can be made most natural and convenient. Next consider if the contemplated solution results in any violations of intuitively expected behavior for edge cases, and how grave the violations are and whether they'll be detected and diagnosed immediately; violations of expected behavior that don't immediately result in an obvious error are to be avoided if at all possible.
 testdriven development or at least no code checkins without adding/running
the necessary tests to/in test_mlabwrap.py.
 rootofallevil: it looks like matlab's engine interface is inherently slow (FIXME elaborate), so there seems little point in complicating code with optimizations unless there is a clear demonstrated need for them. Getting the API design right should be the first priority.
Some concrete goals and plans for v. 1.0 and immediate future
Compatibility
1.0 version should retain compatibility to matlab > 5, python >= 2.3 and
 Numeric as well as numpy (don't break existing code with 1.0 release)
 future versions:
 Numeric compatibility axed immediately after 1.0
compatibility to V >= 6.5 good enough (XXX: when did int types grow arithmetic)?
 require python 2.5 (gives us relative imports, ctypes, withstatements)?
 it will be necessary to keep open the option of incompatible interface changes, but newer versions of mlabwrap should offer a way to get oldstyle behavior (e.g. by using
something like from mlabwrap.v1 import mlab instead of from mlabwrap import mlab)
 Prescriptions for writing upward compatible code: always pass in
float64 arrays (rather than int* arrays) and don't use lists (which may convert to cells in future versions) if you want doubles in matlab.
Installation
Painless Install:
 no setup.py editing required for common scenarios (*XXX* having to set
LD_LIBRARY_PATH is kind of nasty, but I can't see a good way around this)
 no scipy dependency  only external dependency should be numpy and matlab
 cheeseshop support would be nice (see open questions)
Limitations and issue with current design and implementation
mlabraw.cpp  can we use ctypes instead? This could allow for faster development and easier experimentation and due to the high intrinsic overhead the involved speedpenality might not matter at all.
no > 2D support and no proper cell/struct marshaling support (not a hard problem as such; but first one ought to see if migration to ctypes is feasible)
 Conversion behavior. When to proxy and how. When to offer the ability to select/finetune the default behavior, and how.
marshaling behavior (currently: all numeric dtypes to double, all sequences to array); handling of leading/trailing unit dimensions (e.g. _flatten_col_vecs and _flatten_row_vecs)
 Proxy behavior: in particular
a.b.c = d doesn't work as a typical user would expect, although
 this is documented it might well bite unsuspecting users and is the main reason the hybridproxying scheme 2. (see below) makes a proxying for convertible types.
 how should indexing work?
 how much should one make matlab containers look like python containers?
 plain sequence protocol:
x[0] to x(1)
x[1] to x(end)
x.flat[0] to x(1)
len(x) to length(x) (or size(x,1)? or size(x,2)? or numel(x)) length is nasty so size(x,1) would possibly be best
what about iter and in?
 'pseudoarray' protocol
x[multidimensional_array] to ?
x.shape to size(x) (also ndim, imag, real, conj, T,
flat, ravel)
Unfortunately ndarray is a bit bloated, but things that are ubiquitious in matlab, likely to be overloaded for many usertypes and that have a clear ndarray equivalent presumably ought to work (e.g. shape). But what to do about conflicting matlab object properties? Force people to use mlab.subsref(thing, substruct('.', 'shape'))?
 plain sequence protocol:
 generally, to what extent should operator overloading work?
 what about mixed (proxypythonobject) arithmetic?
 how do we handle the intrinsic/extrinsic dimensionality impedence mismatch? Possible solutions include:
 squeezing leading/trailing unit dimensions. Advantage: automatic and cheap; also applicable to marshaling. Difficulty: which one, leading
or trailing? Whilst [[1]] > 1 will typically not cause issues (1x1 matrices are rare), 1 element vectors do commonly occur.
copy matlab's behavior (i.e. x[i] does flat indexing, x[i,j] treats x as a matrix)
inspecting size(x) on indexing x in order to compute the result dimensionality.
 squeezing leading/trailing unit dimensions. Advantage: automatic and cheap; also applicable to marshaling. Difficulty: which one, leading
 Testing
 mlabwrap 1.0 still depends on the obsolete netcdf package for some tests, but the current development version has already switched to a purposebuilt
@proxyTest matlab class
 mlabwrap relies heavily on test driven development but the python standard library unittest is
 illsuited for testing numpy code (because it doesn't provide sensible ways to compare numpy arrays for equality or similarity) and
 generally supoptimal in not supporting interactive, testdriven development properly (during development I want to run tests in ipython and land in pdb when and where something fails, so I can quickly figure out what's going on; and after correcting the code somehow to address the testfailure I want to retry the failed test
first and not wait for all the tests that precede it to complete).
To address 1. test_mlabwrap.py contains some homebrew code to compare arrays, and to address 2. I've written a dropin replacement for unittest that gets used when instead by test_mlabwrap if it is available. However numpy/scipy also contain their own test structure, so it would be good to convert to that and I think Taylor and Jarrod have already started the process. OTOH, from superficial inspections, whilst numpy.testing seems to address 1. it doesn't seem to address 2.  but this is something I'd assume would be convenient for other people as well. Maybe there is a chance of getting something into numpy.testing? Or is what I'm looking for maybe even already available?
 mlabwrap 1.0 still depends on the obsolete netcdf package for some tests, but the current development version has already switched to a purposebuilt
Differences between numpy and matlab that complicate bridging
 more ops
 python lacks the following:
*, /, ^ (instead offering .*, ./, .^)
\, .\
', .'
,, ;
{}, subsindex
kron
any all
set ops: union (could use ''), unique, 'intersect' (could use
'&'), 'setdiff' , 'setxor' , 'ismember' (could use in, but there's a 3 argument version, too)
some bitops: bitget, bitset, the binary version of bitcmp
size (could map to .shape); not quite sure whether numel is somehow
 relevant for mlabwrap
 fastest varying index
 matlab is column major, python is row major; apart from performance penalties when converting this also has implications for how data is preferentially arranged. This also interacts with dimensionality, see below.
 dimensionality
 I can think of two sane and internally consistent ways to handle array dimensionality:
 intrinsic dimensionality
 In numpy dimensionality is intrinsic to an array
(e.g. a = array(1) has dimensionality, i.e. numpy.ndims(a), 0 and a[0,0,0,0] will throw an error).
 sane context dependent dimensionality (scdd)
 In matlab dimensionality is
context dependent (e.g. a=1; a(1,1,1,1) will work fine). A sane way to have done this would be to conceptualize everything as an array with an infinite number of leading (or trailing; if one desires column major) unit dimensions and determine the desired actual dimensionality by context (ignoring leading unit dimensions by default). In other words, under that scheme 1, [1], [[1]], [[[1]]] are all the same object with the same physical representation and when context doesn't determine the dimensionality (e.g. the number of subscripts when indexing), one assumes by default the dimensionality of the arrays sans leading(/trailing) unit dimensions. The (IMO minor) advantage of this scheme is that it is sometimes convenient to regard on and the same object as e.g. a scalar or a 1x1 matrix, depending on context (as is often done in math). The (IMO major) disadvantage is that one looses the ability to regard arrays as nested container types (e.g. in numpy a[0] is legal and has an obvious meaning for any a with nonzero dimensions and it holds that ndims(a[0]) == ndims(a)1. But this equality doesn't hold in scdd and without some arbitrary convention (such as matlab's flatindexing) a[0] is not even meaningful when there is more than one nonunit dimension).
opting for something more messy instead: I think the idea basically is that everything is a matrix, unless it has too many (nonunit trailing) dimensions. As an example, in the 'sane context dependent dimensionality' scheme detailed above ndims(a) would be []; in matlab it is 2, as is ndims(ones(1,1,1)), ndims(ones(2,1,1)), but not ndims(ones(1,1,2)) which is 3. Another annoyance is that matlab isn't really consistent in its columnmajor vantage point: flats (i.e. x(:)) are column vectors, but very basic commands like linspace and the : operator return row vectors  in other words, unlike in numpy there is no 'canonical' vector type; further complicating DWIM conversion attempts.
 dereferencing, nullarycall and indexing
 Matlab doesn't syntactically distinguish between dereferencing a variable and calling a
nullary function  a in matlab can mean a in python, or equally a(). Similarly function call and indexing are syntactically indistinguishable; a(1) could be either a(1) or a[0] in python. One issue where this comes up is determining how mlab.some_var ought to behave.
 Matlab doesn't syntactically distinguish between dereferencing a variable and calling a
 indexing and attribute access and modification

 `{}` vs `()`
currently done with the _ hack; TODO maybe add a way to associate x[key] with {} indexing when x belongs to certain set of classes.
 `subsref` and `subsasgn` are nonrecursive
 By that I mean that whears in
python (only) x.y' gets to handle the attribute access to z in x.y.z`, in matlab it's actually x. Python's behavior becomes an issue with the current (i.e. mlabwrap 1.0) scheme for assigning to.
 1based indexing and `end` arithmetic
(Aside end is pretty nasty; you'd think matlab might just call size to figure out the end for a given dimension, but not so, unless you define your own end method, it just silently uses '1', however not for the a(:) syntax, which one might erroneously assume to resolve to something like a(1:end). Interestingly although I know how to define an end method I haven't figured out how to call it directly...).
 strict slices (matlab) vs permissive ones (python)
[][1:1000] will work fine in python (for arrays and lists), but not in matlab. Although it would be possible to try to hide this (e.g. by doing something like thing(min(slice_start,end),min(slice_end,end)), it's presumably not worth the trouble.
 dtypes
Although matlab has logical (bool) {u,}int{8,16,32,64} as well as single, double and char arrays and therefore a pretty good correspondence to the available numpy dtypes (apart from the fact that {single,double}floats are conflated with {single,double}complex floats), the mapping is complicated by the fact that double takes a very dominant role in matlab (e.g. IIRC the various int types only recently grew even the standard arithmetic operators and have hence largely only been used to represent integral values when using doubles was somehow too expensive or otherwise impossible). Currently mlabwrap "solves" this by just converting everything (save strings) to double, but with matlab's growing emancipation of non 64bit float matrix datatypes, this may become a less attractive tradenoff.
 callbyvalue, copyon write (matlab) vs. proper object identity (python)
 multiple value return
not much of an issue (the nout arg seems to handle this fine)
 broadcasting
 an issue for mixed python/matlab object operations?
Marshaling vs. Proxying
Mlabwrap currently uses two different approaches to make matlab objects available in python: marshaling (i.e. creating an 'equivalent' native python object from a temporary matlaboriginal) for types (currently matrices and strings)) and proxying (creating a proxy object that delegates to the matlab object, which is kept around).
Each method has it's downsides and upsides and the key design questions for the next version of mlabwrap is what mix of the two mlabwrap should employ, how the user can finetune it. Here's some of the issues with various scenarios:
Problems with a puremarshaling scheme
 expressiveness: there will always be types that cannot be marshaled, no matter how sophisticated mlabwrap becomes (e.g. anonymous functions and handles to files or other system resources).
 inefficiencies: deepcopying large structs and in particular objects is quite expensive, especially if one really is only interested in a particular field (struct) or the results of method calls (object). Deepcopying is also not structure preserving, which is not much of a problem in matlab presently since creating shared structure is not straightforward, but this could change as matlab becomes increasingly general purpose.
 breaking interface and encapsulation: marshaling matlab objects to recarrays as suggested in
https://projects.scipy.org/scipy/scikits/wiki/MlabProxyObjects circumvents matlab's equivalent to python's property/__getattr__ mechanisms and such reliance on implementation details is likely to lead to nasty surprises. Generally converting the constituent parts of an matlab object to python equivalents only really makes sense if one is interested in breaking the encapsulation rather than using the intended interface  but that is hardly the case one should optimize for. Additionally such a scheme implicitly assumes 100% roundtripability which seems problematic (XXX: where exactly this assumption might fail is a question worth pondering, irrespective of whether one wants to adopt puremarshaling).
Problems with a pureproxying scheme
 violation of transparency: whilst it might be possible to ducktype ndarrays sufficiently well (possibly autoconverting on certain actions), there are clear limitations, especially for fundamental types such as strings; it is
very unlikely that e.g. a proxied matlab char matrix will be as useful a return value as a str in most situations. Generally the only way to get complete python semantics is to really use native python types.
 inefficiencies: proxying is only more efficient if one doesn't want to 'use' all the data associated with an object in python. For arrays and strings that typically seems unlikely to me.
Hybridscheme 1: pretty much as currently  proxy only objects (and possibly structs), but not arrays, strings etc.
Hybridscheme 2: Also proxy object attributes (on access), even if they could be marshaled (largely so that subattribute assignment can be made to work)
(FIXME expand this section)
Problems with hybridscheme 1
proxy.a.b = c
Problems with hybridscheme 2
surprises: the subtly different behavior of proxy.array and array is going to bite someone somewhere eventually; the question is how often and hard.
 complexity: this scheme is much more complicated than the others proposed here
Summary: I think pure marshaling ought to be available as option (an maybe pureproxying, too), but I suspect that a hybrid approach will make the best default.
Hacks at our disposal to finetune (conversion etc.) behavior
Generally speaking Matlab and python are semantically too different for mlabwrap to be able to offer default behavior that always produces the desired or expected results. Here are ways how finetuning behavior is or could be implemented
 leveraging python's richer syntax
keyword arguments (e.g. nout)
 nasty: use the fact that names may not begin with '_' in matlab to give
mlab.foo different semantics from mlab._foo; currently this is only used to handle python keywords (e.g. mlab._print) and {} indexing.
customization variables (e.g. _array_cast, _flatten_col_vecs)
 Downside: python's weak support for dynamic scope makes this unattractive (by and large anything governing pervasive behavior (e.g. number of significant digits in computations; printing precision; floating modes etc.) ought to be dynamically scoped; statically scoped global vars as in python
suck; however python 2.5's with statement can be used as a (poor man's?) fluidlet). It should also be borne in mind that the more customization switches there are the harder it becomes to read code using mlabwrap because one has to find out which switches are in effect in order to interpret it correctly.
 Downside: python's weak support for dynamic scope makes this unattractive (by and large anything governing pervasive behavior (e.g. number of significant digits in computations; printing precision; floating modes etc.) ought to be dynamically scoped; statically scoped global vars as in python
 proxying with transparent autoconversion
As hinted above too much flexibility can be a bad thing; the less customization possibilities the design needs whilst retaining generality and convenience for the common cases, the better.
Relevant Links
rpy and other pythonx bridges
 should be studied for design ideas
Open questions
does setup.py work under windows as desired?
Is guessing the default nout of builtins via the horrible docstring regexp
hack (expound_docstring in dev. version) still needed for nonancient matlab versions?
distutils vs. numpy.distutils vs. setuptools (ADDENDUM: apparently http://cheeseshop.python.org/pypi/setuptools is more uptodate):
 version 1.0 will use plain distutils
 for future versions:
is there a (sane) way to install automatically, even if numpy is not already installed? We need numpy.get_includes (or numpy.distutils equivalent) for options to pass to setup but setup is also the place where the dependency on numpy is declared (?