smop 0.25.1

Matlab to Python compiler

SMOP stands for Small Matlab/Octave to Python compiler. It converts matlab and octave programs to python. The resulting .py program imports runtime.py, which contains the necessary runtime support – several class definitions and about 30 small everyday functions, such as length.

This matlab program solver.m was taken from the matlab programming competition in 2004 (Moving Furniture). To the right is a.py – its SMOP translation to python.

01   function mv = solver(ai,af,w)                01 def solver_(ai,af,w,nargout=1):
02   nBlocks = max(ai(:));                        02     nBlocks=max_(ai[:])
03   [m,n] = size(ai);                            03     m,n=size_(ai,nargout=2)
04   I = [0  1  0 -1];                            04     I=matlabarray([0,1,0,- 1])
05   J = [1  0 -1  0];                            05     J=matlabarray([1,0,- 1,0])
06   a = ai;                                      06     a=copy_(ai)
07   mv = [];                                     07     mv=matlabarray([])
08   while ~isequal(af,a)                         08     while not isequal_(af,a):
09     bid = ceil(rand()*nBlocks);                09         bid=ceil_(rand_() * nBlocks)
10     [i,j] = find(a==bid);                      10         i,j=find_(a == bid,nargout=2)
11     r = ceil(rand()*4);                        11         r=ceil_(rand_() * 4)
12     ni = i + I(r);                             12         ni=i + I[r]
13     nj = j + J(r);                             13         nj=j + J[r]
14     if (ni<1) || (ni>m) || (nj<1) || (nj>n)    14         if (ni < 1) or (ni > m) or (nj < 1) or (nj > n):
15         continue                               15             continue
16     end                                        16
17     if a(ni,nj)>0                              17         if a[ni,nj] > 0:
18         continue                               18           continue
19     end                                        19
20     [ti,tj] = find(af==bid);                   20         ti,tj=find_(af == bid,nargout=2)
21     d = (ti-i)^2 + (tj-j)^2;                   21         d=(ti - i) ** 2 + (tj - j) ** 2
22     dn = (ti-ni)^2 + (tj-nj)^2;                22         dn=(ti - ni) ** 2 + (tj - nj) ** 2
23     if (d<dn) && (rand()>0.05)                 23         if (d < dn) and (rand_() > 0.05):
24         continue                               24             continue
25     end                                        25
26     a(ni,nj) = bid;                            26         a[ni,nj]=bid
27     a(i,j) = 0;                                27         a[i,j]=0
28     mv(end+1,[1 2]) = [bid r];                 28         mv[mv.shape[0] + 1,[1,2]]=[bid,r]
29  end                                           29
30                                                30     return mv

Though only 30 lines long, this example shows many of the complexities of converting matlab code to python.

line
02	Matlab uses round brackets both for array indexing and for function calls. To figure out which is which, SMOP computes local use-def information, and then applies the following rule: undefined names are functions; defined, are arrays.
03	Matlab function size returns variable number of return values. In python, functions are usually unaware of the expected number of return values. To solve this, number of return values is explicitly passed in nargout.
04	Matlab array indexing starts with 1, python starts with zero. New class matlabarray derives from ndarray, but exposes matlab array behaviour.
06	Matlab array assignment implies copying; python assignment implies data sharing. We use explicit copy here.
07	Empty matlabarray object is created, and then extended at line 28.
09	Matlab functions of zero arguments can be used without the parentheses, such as rand.
10	Matlab function find returns variable number of values, which is explicitly passed in nargout.
12	Variables I and J contain matlab-style arrays.

Command-line options

lei@dilbert ~/smop-github/smop $ python main.py -h
SMOP compiler version 0.25.1
Usage: smop [options] file-list
    Options:
    -V --version
    -X --exclude=FILES      Ignore files listed in comma-separated list FILES
    -d --dot=REGEX          For functions whose names match REGEX, save debugging
                            information in "dot" format (see www.graphviz.org).
                            You need an installation of graphviz to use --dot
                            option.  Use "dot" utility to create a pdf file.
                            For example:
                                $ python main.py fastsolver.m -d "solver|cbest"
                                $ dot -Tpdf -o resolve_solver.pdf resolve_solver.dot
    -h --help
    -o --output=FILENAME    By default create file named a.py
    -o- --output=-          Use standard output
    -s --strict             Stop on the first error
    -v --verbose