Using Python as a wrapper or interface
Python has gained popularity for implementing scientific computations, partly because of its rather-convenient occasionally-Fortran-looking syntax as opposed C/C++ languages, but more recently, because of the vast number of scientific libraries that are nowadays available in Python.
Nevertheless, the execution speed of a Python code is significantly lower than what can be obtained by programming in languages such as Fortran, C, or C++. For example, see the following performance comparisons and tests in NASA modeling guru webpage or the updated version here. As you can see there, the performance of Python code can be significantly lower, up to 500 times and more, compared to compiled languages such as Fortran and C. These languages compile the program to machine language, which enables the computing resources to be utilized with very high efficiency. Knowing the performance hit in Python, the scientific programming paradigm in Python is to write compute-intensive parts of the code in lower level languages such as Fortran or C and use Python as wrapper and glue between lower level codes and as a handy tool for high-level tasks.
Python was initially designed for being integrated with C. This feature has spawned the development of several techniques and tools for calling compiled languages from Python, allowing us to relatively easily reuse fast and well-tested scientific libraries in Fortran, C, or C++ from Python, or migrate slow Python code to compiled languages. It often turns out that only smaller parts of the code, usually for loops doing heavy numerical computations, suffer from low speed and can benefit from being implemented in Fortran, C, or C++.
There are already several Python wrappers developed for integrating Python with other programming language codes. Most prominent examples include F2PY for Fortran and C codes, SWIG for C, C++, Perl, Java, and many others, Cython for C, Jython for Java, and several others.
The usage of some of these wrappers can be tricky and requires some work and good familiarity with the wrapper. This is, in particular, true about SWIG, which involves a significant amount of manual modifications to the interfaces, compared to F2PY, for example. At the moment, F2PY only works with Python 2.x standard.
There is also a Python module pymat developed for direct interaction of Python code with MATLAB.