compile
- Python course
- Expert
- Lesson 17/47
- 5 min
Learn to turn AST into executable code with compile().
What is compile?
compile turns an AST or a code string into an executable code object. It takes three arguments: source, filename and mode ("exec", "eval" or "single").
Mode "exec" runs multiple statements; "eval" evaluates a single expression. You run the resulting code object with exec or eval. Transforming an AST and recompiling it is a powerful technique for code generation and macro-like tools.
From AST to code object
You compile an AST with compile(tree, "<test>", "exec"). The second argument is the filename; it shows up in error messages, usually a name like "<test>". The third is the mode.
You run the resulting code object with exec(code, ns) in a namespace. The ns dict holds variables; you access them with ns["result"]. This flow — parse, transform, compile, run — is the classic chain of code-processing tools. It is flexible because each step is separately controllable.
Practice Run an AST with compile
Import the module with import ast. Build the tree with ast.parse("sonuc = 6 * 7"). Produce a code object with compile(tree, "<test>", "exec"). Run exec(code, ns) in an ns = {} dict and print ns["sonuc"].
Starter code
# compile the tree and run it
# print the resultSample solution
import ast
tree = ast.parse("sonuc = 6 * 7")
code = compile(tree, "<test>", "exec")
ns = {}
exec(code, ns)
print(ns["sonuc"])Expected output
42
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match compile concepts
| Term | Meaning |
|---|---|
compile |
Turns into code |
exec |
Multiple statements |
eval |
Single expression |
code object |
Executable |
2 Complete the compile call
code = ____(tree, "<test>", "exec")code = compile(tree, "<test>", "exec")Explanation: compile(tree, file, mode) produces a code object.
3 What does compile mode 'exec' do?
code = compile("x = 1
y = 2", "<t>", "exec")
ns = {}
exec(code, ns)
print(ns)- Raises an error
- Runs multiple statements Correct answer
- Evaluates one expression
- Returns only a constant
Explanation: 'exec' mode runs multiple statements; 'eval' is for a single expression.