General coding rules====================This section provides lists of general coding rules for the GammaLibdevelopment.C++ rules---------All GammaLib C++ code must be compatible with ISO standard C++98.Do not use C++11 features.(see hereif you don't know what C++98 and C++11 is and note that C++03 isjust a minor correction of C++98).The reason for this restriction is that C++ compilers / standard librariessuch as gcc / libstdc++or clang / libc++only finished implementing C++11 in 2013 and using C++11 features in GammaLib wouldmake it impossible to use GammaLib on user and server machines with an old compiler.Code format^^^^^^^^^^^- Blocks are indented by 4 characters.- Do not use tabs (code formatting should be independent of editor configurations).- Do not exceed a line length of 80 characters (a few more characters are acceptable in exceptional cases).- Put a blank line at the end of each file (this is required by some compilers).- Each function starts with a curly bracket in the line following the function name. The return type is in the same line as the function name. Example: .. code-block:: cpp int function(void) { int i = 0; ... return i; }- Code blocks should be encompassed in curly brackets, even if the block consists only of a single line.- The opening curly bracket of a block starts in the same line as the related statement. Example: .. code-block:: cpp for (int i = 0; i < 10; ++i) { sum += i; }- Separate code elements by spaces; for example, do not write int i=0; but write int i = 0;.- Align successive similar lines on common elements. Here a common example illustrating the alignment on the = symbol: .. code-block:: cpp m_max = par.m_max; m_prompt = par.m_prompt; sum += par.m_sum; And here an example illustrating the alignment in a class definition on the member function name: .. code-block:: cpp void log10GeV(const double& eng); void log10TeV(const double& eng); std::string print(void) const;Code semantics^^^^^^^^^^^^^^- Each function and/or method terminates with a return statement.- Each function and/or method has only a single exit point (i.e. a single return statement).- Use explicit for constructors with single arguments to prevent unintended type conversions. The only exception to this rule is the copy constructor or type conversion constructors.- Specify void for function definitions without arguments, i.e. use void function(void) instead of void function() in the function declaration.- Use pre-incrementation in loops (pre-incrementation is faster than post-incrementation). Example: .. code-block:: cpp for (int i = 0; i < 10; ++i) { sum += i; }- Where possible (and appropriate), use std::vector containers instead of allocating memory. In other words: avoid direct memory allocation with new.- Use the std:: namespace prefix where possible; write for example .. code-block:: cpp std::sin(angle); std::cos(angle); You may not believe it, but droping the std:: may on some systems lead to considerably slower code for trigonometric functions!- Provide comments, comments, comments!!!Language features^^^^^^^^^^^^^^^^^- Do not use macros.- Do not use #define directives for the declaration of constants. Use const instead.- Do not use std::strncpy, std::memcpy or similar as these functions are corrupted on some systems.- If possible, pass arguments by reference.- Output arguments should be passed as pointers.- Use C++ (std::string) instead of C-style (char*) strings.- Use C++ casts instead of C-style casts.- Avoid using templates.Python rules------------All code must be compatible with Python 2.6, 2.7 as well as 3.2 or later.As of 2014 most users still have Python 2, even though Python 3 has beenout for five years, so using Python 3 features is out of the question.Also GammaLib is mostly a C++ library with only some high-level analysisscripts (e.g. running a complete simulation or analysis or plotting some results)that are simple Python code and wouldn't profit much from using new Python 3 features.Code format^^^^^^^^^^^- Python code should follow the official PEP8 Python style: It says (among many other things) that you should indent with four spaces, not tabs. Following PEP8 is simple, because there's a pep8 tool that you should run on your Python code before committing, e.g. like so: .. code-block:: bash $ pep8 test/test_python.py ... test/test_python.py:156:1: W191 indentation contains tabs test/test_python.py:156:1: W391 blank line at end of file test/test_python.py:156:1: W293 blank line contains whitespace $ If you want you can even use the autopep8 tool which can automatically fix the formatting for almost all cases. Run pep8 -h and autopep8 -h to see the options you can use. PEP8 compliance is automatically checked by the continuous integration system.Code semantics^^^^^^^^^^^^^^- When writing scripts, the following import conventions should be used:: >>> import gammalib >>> energy = gammalib.GEnergy(10, 'TeV') >>> import numpy as np >>> import matplotlib.pyplot as plt In interactive sessions (IPython is recommended) to save typing you can use import * to import everything into your local namespace:: >>> from gammalib import * >>> energy = GEnergy(10, 'TeV') >>> from numpy import * >>> from matplotlib.pyplot import * Using import * in Python scripts is not recommended. Some reason are given in this section in the Python docs. - Most GammaLib code can be written equivalently in C++ and / or Python, however some things have been made "Pythonic" in the SWIG Python wrapper. GammaLib objects can be printed by passing them to the Python print function. GammaLib container classes feature a Pythonic list-like interface, i.e. they can be iterated over and elements can be accessed with []. Examples: .. code-block:: python # Create a container with two elements >>> from gammalib import GEnergy, GEnergies >>> energies = GEnergies() >>> energies.append(GEnergy(1, 'TeV')) >>> energies.append(GEnergy(3, 'TeV')) # Print GammaLib object Python-style. # C++ style would be calling a member function: energies[1].print() >>> print(energies[1]) 2 TeV # Use the container like a Python list >>> len(energies) 2 >>> for energy in energies: print(energy) 1000 GeV 2 TeVLanguage features^^^^^^^^^^^^^^^^^You can find lots of information on how to write Python code that work withPython 2 and 3 on the web, e.g.hereand here.If you don't have a Python 2 or Python 3 interpreter on your developmentmachine, don't worry. This will be checked during code review or duringcontinuous integration testing.The most common Python 2 / 3 issues are print and integer division.- You should use the print() function, because the print statement was removed in Python 3:: >>> print('hello') # print function. Good. Works in Python 2 and 3. hello >>> print 'hello' # print statement. Bad. Only works in Python 2. SyntaxError: invalid syntax- Integer division behaves differently in Python 2 and 3. >>> 5 / 2 # Python 3: integer division results in float 2.5 >>> 5 / 2 # Python 2: integer division results in int 2 If you do need integer division in your Python code, you should use one of these explicit forms that work in Python 2 and 3:: >>> int(5 / 2) # Python 2 and 3: truncate int part 2 >>> 5 // 2 # Python 2 and 3: integer division 2A good way to enforce Python 3 compatible behaviour in your scriptconcerning print and integer division even when running it in Python 2is to put the following line at the top of your Python script: .. code-block:: python from __future__ import print_function, division