compile()

compile(source, filename, mode, flags=0, dont_inherit=False, optimize=-1)

The compile() function takes source code as a string or AST object and returns a code object. This code object can then be passed to exec() or eval() for execution. It’s useful for dynamically generating and executing Python code at runtime.

Syntax

compile(source, filename, mode, flags=0, dont_inherit=False, optimize=-1)

Parameters

Parameter	Type	Default	Description
source	str or AST	—	A string containing Python source code, or an AST object
filename	str	—	The filename used in error messages; typically <string> for inline code
mode	str	—	One of 'exec', 'eval', or 'single'
flags	int	0	Controls which future statements affect the compilation; use __future__ module constants
dont_inherit	bool	False	If True, ignores inherited future statements
optimize	int	-1	Optimization level: -1 (default), 0 (no opt), 1 (-O), 2 (-OO)

Mode Values

Mode	Use For
'exec'	Executing a statement or a sequence of statements
'eval'	Evaluating a single expression
'single'	Executing a single statement (like a REPL)

Examples

Basic usage with exec

source_code = """
def greet(name):
    return f"Hello, {name}!"

message = greet("World")
print(message)
"""

compiled = compile(source_code, "<string>", "exec")
exec(compiled)
# Hello, World!

Using eval with an expression

expression = "2 + 3 * 4"
compiled_expr = compile(expression, "<string>", "eval")

result = eval(compiled_expr)
print(result)
# 14

Dynamic function creation

source = """
def add(a, b):
    return a + b
"""

code = compile(source, "<string>", "exec")
namespace = {}
exec(code, namespace)

add_function = namespace["add"]
print(add_function(5, 3))
# 8

Using flags for future statements

from __future__ import annotations

source = """
def foo(x: int) -> int:
    return x * 2
"""

code = compile(source, "<string>", "exec", flags=0, dont_inherit=False)

Error handling with compile

bad_source = """
def broken(
    return 42
"""

try:
    compile(bad_source, "<string>", "exec")
except SyntaxError as e:
    print(f"Syntax error at line {e.lineno}: {e.msg}")
# Syntax error at line 3: invalid syntax

Single mode for REPL-like behavior

source = "x = 5"
code = compile(source, "<string>", "single")

namespace = {}
exec(code, namespace)
print(namespace["x"])
# 5

Common Patterns

Template-based code generation

template = """
def {func_name}({params}):
    \"\"\"Auto-generated function\"\"\"
    return {result}
"""

source = template.format(
    func_name="multiply",
    params="a, b",
    result="a * b"
)

code = compile(source, "<string>", "exec")
namespace = {}
exec(code, namespace)

print(namespace["multiply"](3, 7))
# 21

Conditional code execution

debug_mode = True

code = compile("print('Debug info')" if debug_mode else "pass", "<string>", "exec")
exec(code)
# Debug info

Compiling AST objects

import ast

source = "print('Hello from AST')"
tree = ast.parse(source)
compiled = compile(tree, "<string>", "exec")
exec(compiled)
# Hello from AST

Errors

Error	When
SyntaxError	Source code has invalid Python syntax
TypeError	source is not a string or AST object, or mode is invalid
ValueError	flags contains invalid bit values

See Also

• exec() — execute dynamically compiled code
• eval() — evaluate a dynamically compiled expression