Automated style checking#

The easiest way to enforce the SUMO code style for C++ and Python is to enable the pre-commit checks.

C++ Code#

We try to have the code compatible to a wide range of C++11 compatible compilers and test every commit / pull request against gcc and clang on macOS and Linux, and Visual Studio 2015 - 2022 on Windows. For the C++ code we use AStyle to keep indentation and other whitespace usage consistent throughout the project. In order to make your code appear same as the original SUMO code use the following call to AStyle (or execute tools/build_config/ --fix <FILE_NAME> before committing):

astyle --style=java --unpad-paren --pad-header --pad-oper --add-brackets --indent-switches --align-pointer=type -n <FILE_NAME>

Still, there are several other things you should keep in mind (The Google C++ Style Guide is a good read as well):


Use the following templates for your files:


  • Never use tab stop. Always use 4 spaces for indentation. In Visual Studio tab stop can be disabled in Tools/Options/Text Editor/All languages/Tabs.

Class Names#

  • All class names must start with capital letter
  • The first capital letters of a class should be used to indicate their module (NBEdge -> Net Build module, MSChargingStation -> Micro Simulation module
  • If a class name is composed of multiple words, every word must start with capital letter (Micro simulation charging station -> MSChargingStation)
  • please do not arbitrarily introduce new namespaces

Variable Names#

  • Variables used within methods should be named using "camel-caps", f.e. "currentCarVelocity"
  • Member variables should additionally have the prefix "my", f.e. "myMaximumVehicleVelocity"
  • try not to abbreviate variable names (myMaximumVehicleVelocity instead of myMVV)
  • give names to variables which describe its purpose within the context
  • do not reuse variables for different purposes


  • All enum names must start with capital letter, and If their name is composed of multiple words, every word must start with capital letter
  • Every definition must be written using capital letters (SumoXMLTag { SUMO_TAG_EDGE, SUMO_TAG_LANE, ... } )


Only use the plain ASCII characters in cpp and h files. (0x20 - 0x7E). If you need to convey extended character information use TeX or HTML notation instead.


  • do not use backslashes (\)! use slashes (/) only
  • do not use absolute paths!; something like #include "/home/daniel/mylibs/include_me.h" will never work somewhere else! Use relative paths and tell the compiler where the other libraries may be found. If you have problems on this, please tell us, we'll write some further documentation!
  • in general we mention the standard library includes first (like #include <vector>), then the includes of libraries used by SUMO (FOX / Xerces) and later our own headers
  • brackets ("<" and ">") are preferred for files not residing in the same directory, while quotation marks are usually used for files in the same directory.

"using namespace ..."-statements#

  • Avoid them whenever possible and especially do not use "using namespace ..."-statements within the .h-files! It's possible that an included library tries to use a different implementation - who knows? Using a "using namespace ..."-statement within your .h-file may yield in an unexpected behavior.


Object Handling#

  • If the structure you are implementing has an id, then derive the object from Named (<SUMO_HOME>/src/utils/common/Named.h). This class supports the std::string getID()-method.
  • If you want to store something in a map pointing from string ids to object instances, then use NamedObjectCont (<SUMO_HOME>/src/utils/common/NamedObjectCont.h).

Integer Types#

  • Use simple int whenever possible. There are probably lots of places in the sumo code which rely on the fact that this has at least 32 bits, so you may too.
  • Try to avoid unsigned ints whenever possible. It is sometimes not possible when calling Xerces-C and GL functions or using std::string::npos but try to limit it to those cases.
  • If you need at least 64 bit, use long long int.


  • Do not use redundant condition checks. Example: if (myCondition) instead of if (myCondition == true)


  • Use the C++ 11 range loop syntax whenever possible. Example: for (element& it : myContainer) instead of for (container::iterator it = myContainer.begin(); it != myContainer.end(); it++). Still try to name the element type explicitly instead of using "auto" at least when iterating over lists / vectors.

Python Code#

We try to adhere to the PEP 8 Style Guide and use autopep8 and flake8 to check this. If you have both modules installed, you can run tools/build_config/ <FILENAME> to check this and also fix some of the errors. We run both tools without any special options except for the line length which we limit to 120.

Please remember to make your file executable if (and only if) the file should be executable (i.e. is not a module to be imported by others). Windows users please follow this recipe. Executable files should also contain a so called shebang in the first line:

!#/usr/bin/env python

If your script needs Python 3 then state python3 there.

Python2 / Python3 compatibility#

Our main development focuses on Python 3.7 and later but we strive for Python 2 compatibility. When writing or editing scripts, keep the following in mind:

  • use print as a function (from __future__ import print_function)
  • use items instead of iteritems, which will return a list under Python 2.7 and an iterator in Python 3 (for item in dict.items())
  • use values instead of itervalues, which will return a list under Python 2.7 and an iterator in Python 3 (for val in dict.values())
  • use // instead of / for integer division because / will do a floating point division under Python 3 (4/3 = 1.3333333)
  • the floating point division with / can be included in Python 2 by (from __future__ import division)
  • while iterating over unsorted lists or iterators Python 2 and Python 3 do not work in the same order. Therefore add a explicit sorted before iteration when you write e.g. a xml file (for item in sorted(list))
  • use the argparse library instead of optparse (which is deprecated). The use of most functions stayed the same, only some names differ. For further information please check
  • if you want to use different code for Python 2 and Python 3, which can be necessary since not all libraries exist for both versions, you can use a simple if else statement with the PY3 boolean defined by(PY3 = sys.version_info > (3,))
  • use byte type in Python 3 wherever you use binary data and string type wherever you used unicode strings before. This can be made by if else statements using the PY3 boolean. See a list for the different methods possible on bytes and strings at

For further information about possible error sources and difficulties resulting in Python 3 compatibility see also and


Use the following template for your files:

Line endings and keyword replacement#

We enforce special line endings for the following file types (overriding core.autocrlf settings of git) using <SUMO_HOME>/.gitattributes:

  • LF for
    • source files (".h", ".cpp", ".py", ...),
    • Test files (".xml", ".prog", ".complex", ".dfrouter", ".duarouter", ".jtrrouter", ".netconvert", ".sumo", ".meso", ...)
  • CRLF for Windows only files (".bat", ".props", ".vcxproj", ".filters", ...)

Git has no equivalent to the svn:keywords property, so we do not use the $Id$ keyword any longer.