Global variables are immutable.

for statements are not allowed at the top-level. Use them within functions instead. In BUILD files, you may use list comprehensions.

if statements are not allowed at the top-level. However, if expressions can be used: first = data[0] if len(data) > 0 else None.

Deterministic order for iterating through Dictionaries.

Recursion is not allowed.

Int type is limited to 32-bit signed integers. Overflows will throw an error.

Modifying a collection during iteration is an error.

Except for equality tests, comparison operators <, <=, >=, >, etc. are not defined across value types. In short: 5 < 'foo' will throw an error and 5 == "5" will return false.

In tuples, a trailing comma is valid only when the tuple is between parentheses, e.g. write (1,) instead of 1,.

Dictionary literals cannot have duplicated keys. For example, this is an error: {"a": 4, "b": 7, "a": 1}.

Strings are represented with double-quotes (e.g. when you call repr).

Strings aren’t iterable.

implicit string concatenation (use explicit + operator).

Chained comparisons (e.g. 1 < x < 5).

class (see struct function).

import (see load statement).

while, yield.

float and set types.

generators and generator expressions.

lambda and nested functions.

is (use == instead).

try, raise, except, finally (see fail for fatal errors).

global, nonlocal.

most builtin functions, most methods.