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Python code conventions

Python code follows PEP 8.

Naming conventions:

  • Module names are short and all lowercase; eg pyb, stm.
  • Class names are CamelCase, with abreviations all uppercase; eg I2C, not I2c.
  • Function and method names are all lowercase with words separated by a single underscore as necessary to improve readability; eg mem_read.
  • Constants are all uppercase with words separated by a single underscore; eg GPIO_IDR.

C code conventions

When writing new C code, please adhere to the following conventions.

White space:

  • Expand tabs to 4 spaces.
  • Don't leave trailing whitespace at the end of a line.
  • For control blocks (if, for, while), put 1 space between the keyword and the opening parenthesis.
  • Put 1 space after a comma, and 1 space around operators.


  • Use braces for all blocks, even no-line and single-line pieces of code.
  • Put opening braces on the end of the line it belongs to, not on a new line.
  • For else-statements, put the else on the same line as the previous closing brace.

Header files:

  • Header files should be protected from multiple inclusion with #if directives. See an existing header for naming convention.


  • Use underscore_case, not camelCase for all names.
  • Use CAPS_WITH_UNDERSCORE for enums and macros.
  • When defining a type use underscore_case and put '_t' after it.

Integer types: MicroPython runs on 16, 32, and 64 bit machines, so it's important to use the correctly-sized (and signed) integer types. The general guidelines are:

  • For most cases use mp_int_t for signed and mp_uint_t for unsigned integer values. These are guaranteed to be machine-word sized and therefore big enough to hold the value from a MicroPython small-int object.
  • Use size_t for things that count bytes / sizes of objects.
  • You can use int/uint, but remember that they may be 16-bits wide.
  • If in doubt, use mp_int_t/mp_uint_t.


  • Be concise and only write comments for things that are not obvious.
  • Use // prefix, NOT /* ... */. No extra fluff.

Memory allocation:

  • Use m_new, m_renew, m_del (and friends) to allocate and free heap memory. These macros are defined in py/misc.h.


Braces, spaces, names and comments:

#define TO_ADD (123)

// This function will always recurse indefinitely and is only used to show
// coding style
int foo_function(int x, int some_value) {
    if (x < some_value) {
        foo(some_value, x);
    } else {
        foo(x + TO_ADD, some_value - 1);

    for (int my_counter = 0; my_counter < x; my_counter++) {

Type declarations:

typedef struct _my_struct_t {
    int member;
    void *data;
} my_struct_t;