pycparser

Warnings

• breaking v3.0 dropped PLY entirely and rewrote the lexer/parser from scratch. CParser.__init__ kwargs lex_optimize, yacc_optimize, yacc_debug, lextab, yacctab are no longer accepted — passing them raises TypeError.
  Fix: Remove all PLY-related kwargs from CParser() calls. The public AST API is unchanged; only internal constructor arguments differ.
• breaking Python 3.8 support was dropped in v3.0. Requires Python >=3.10.
  Fix: Upgrade to Python 3.10+. Pin pycparser<3 if you must support Python 3.8 or 3.9.
• gotcha pycparser cannot parse raw C files that contain #include or macros — it requires preprocessed input. Passing unpreprocessed C to parser.parse() will produce parse errors for any non-trivial real-world file.
  Fix: Use parse_file(..., use_cpp=True) which calls cpp/gcc-E automatically, or manually preprocess with subprocess before calling parser.parse().
• gotcha fake_libc_include headers are NOT included in the PyPI pip wheel. Code that assumes pycparser.__file__ contains a utils/fake_libc_include directory will fail at runtime.
  Fix: Install the companion package `pip install pycparser-fake-libc` and use `import pycparser_fake_libc; cpp_args='-I' + pycparser_fake_libc.directory`, or vendor the headers from the GitHub source tree.
• gotcha The fake_libc_include headers target C11 and will cause errors if the preprocessor is invoked with -std=c99 or older standards.
  Fix: Omit -std=c99 from cpp_args when using fake_libc_include, or use a preprocessor invocation that defaults to C11 or later.
• gotcha pycparser supports C99 and a subset of C11, but does NOT support GCC/Clang extensions (__attribute__, __extension__, __builtin_*, etc.) out of the box. Passing GCC-extended code will raise ParseError.
  Fix: Pass cpp_args=['-D__attribute__(x)=', '-D__extension__=', ...] to strip extensions before parsing, as shown in the project FAQ.
• gotcha Frozen-app packagers (cx_Freeze, PyInstaller) may fail to import pycparser 3.0 due to internal relative-import restructuring introduced when PLY was removed, raising ImportError on 'c_parser'.
  Fix: Check for updated hooks in your freezer tool. As a workaround, pin pycparser<3 until the packager adds support.

Install

• pip install pycparser Latest (3.x, no-dependency)
• pip install "pycparser<3" Legacy PLY-based 2.x (Python 3.8+)

Imports

• CParser

  from pycparser import c_parser
  parser = c_parser.CParser()

  CParser lives in the c_parser submodule; top-level pycparser does not re-export it directly.
• parse_file

  from pycparser import parse_file

  parse_file IS exported from the top-level package and invokes cpp/gcc-E automatically.
• c_generator.CGenerator

  from pycparser import c_generator
  gen = c_generator.CGenerator()

  Used to emit C source from a pycparser AST; must be imported from the submodule.
• c_ast / NodeVisitor

  from pycparser import c_ast
  class MyVisitor(c_ast.NodeVisitor): ...

  All AST node types and the NodeVisitor base class live in pycparser.c_ast.

Quickstart

Parse a tiny C snippet directly with CParser (no preprocessor needed for self-contained code), then walk the AST with a visitor.

from pycparser import c_parser, c_ast, c_generator

# Direct in-memory parse — only works for preprocessor-free, self-contained C
parser = c_parser.CParser()

src = r"""
int add(int a, int b) {
    return a + b;
}
"""

ast = parser.parse(src, filename='<none>')
ast.show(attrnames=True, nodenames=True)

# Regenerate C source from AST
gen = c_generator.CGenerator()
print(gen.visit(ast))

# Visitor pattern: collect all function names
class FuncDefVisitor(c_ast.NodeVisitor):
    def visit_FuncDef(self, node):
        print('Function:', node.decl.name)

v = FuncDefVisitor()
v.visit(ast)