Check syntax error python

How to Check Syntax Errors in Python Code ?

Option 1 — Using Compilation Script :

• Using Python basic compilation . Use the code below and save it as any .py file e.g pythonSyntaxChecker.py

 import sys your\_python\_script\_name = sys.argv\[1\] source = open(your\_python\_script\_name, 'r').read() + '\\n' compile(source, your\_python\_script\_name, 'exec') 

 python3 pythonSyntaxChecker.py yourPythonScript.py OR python pythonSyntaxChecker.py yourPythonScript.py 

Option 2 — Using Direct Compilation :

• You can directly compile your Python script
• Note the below poinst —
  • python returns a non-zero exit code if the compilation fails.
  • Also type errors are not detected — those are only detected at runtime

   python -m py\_compile yourPythonScript.py 

  Option 3 — Using Pychecker :

    pychecker \[options\] YOUR\_PYTHON\_SCRIPT.py 

  • The [options] provides below features —
    • —only —> only warn about files passed on the command line
    • -#, —limit —> the maximum number of warnings to be displayed
    • —no-shadowbuiltin —> check if a variable shadows a builtin
    • -q, —stdlib —> ignore warnings from files under standard library
    • -T, —argsused —> unused method/function arguments

     script1.py:5: Imported module (string) not used script1.py:6: Instantiating an object with arguments, but no constructor script1.py:7: Object (useless) has no attribute (valeu) script1.py:8: No local variable (var1) script1.py:9: self is not first method argument 

    Option 4 — Using Pyflakes :

     pyflakes yourPythonScript.py 

    Option 5 — Using «ast» module

    • The ast module helps to process trees of the Python abstract syntax grammar — basically ast helps to find out the current grammar appearance.
    • More here — https://docs.python.org/3/library/ast.html
    • Using CLI

     python -c "import ast; ast.parse(open('yourPythonScript.py').read())" 

     import ast tree = ast.parse("print ('This is Great')") ast.dump(tree) "Module(body=\[Expr(value=Call(func=Name(id='print', ctx=Load()), args=\[Str(s='This is Great')\], keywords=\[\]))\])" 

     import ast, traceback g = '' with open(g) as f: source = f.read() valid = True try: ast.parse(source) except SyntaxError: valid = False traceback.print\_exc() finally: print(valid) ast.dump(source) 

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    Python syntax checker

    Python checker allows to check your Python code syntax (Python 3), and find Python errors. This Python code checker tool highlights and goes to line with a syntax error.

    To check your code, you must copy and paste, drag and drop a Python file or directly type in the Online Python editor below, and click on «Check Python syntax» button.

    You can see the user guide to help you to use this python checker tool.

    User guide

    • First, Drag and drop your Python file or copy / paste your Python text directly into the editor above.
    • Finally, you must click on «Check Python syntax» button to start code checking.

    It is quick and easy to analyze python code!

    Python code checker tool

    Python is a server-side scripting language, but can also be used as a general-purpose programming language.

    Python error checker tool allows to find syntax errors (lint). You can test your Python code online directly in your browser.

    If a syntax error is detected, then the line in error is highlighted, and it jumps to it to save time (no need to search the line).

    It can be useful to make online test to save time (deployment . ).

    Note: This tool no longer offers sandbox, it was not good enough.

    About Python

    Python is an interpreted programming language, it features a dynamic type system and automatic memory management (garbage collector). Python is available for many operating systems.It has a large standard library.

    Python formatting is visually uncluttered, and often uses English keywords rather than punctuation. Python uses whitespace indentation instead of curly brackets to delimit blocks.

    Python is often used as a programming language in high school and higher education, especially in France (I am French).

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    Check syntax error python

    Last updated: Jun 13, 2023
    Reading time · 5 min

    

    # Table of Contents

    # Check the syntax of a Python script without executing it

    You can check the syntax of a Python script without executing it by compiling the file.

    The py_compile module will compile the specified files and will alert you if you have syntactical errors.

    Suppose you have the following Python script named main.py .

    Copied! 
    if 10 > 5: print('bobbyhadz.com') 

    You can check the syntax of the script without executing it by running the following command in your terminal.

    Copied! 
    python -m py_compile main.py # or with python3 python3 -m py_compile main.py 

    Make sure to replace main.py with the name of your Python script.

    

    As shown in the screenshot, no errors are reported because the syntax in the main.py file is valid.

    Let’s comment out the call to the print function.

    Copied! 
    if 10 > 5: # print('bobbyhadz.com') 

    The file has a syntactical error because we didn’t add any code to the if block and didn’t use a pass statement.

    Let’s run the py_compile command again.

    Copied! 
    python -m py_compile main.py # or with python3 python3 -m py_compile main.py 

    

    Running the command produces the following output:

    Copied! 
    Sorry: IndentationError: expected an indented block after 'if' statement on line 1 (main.py, line 2) 

    When the py_compile module is run as a script, it compiles all of the specified files.

    If one or more of the files cannot be compiled, a non-zero exit status is returned.

    You can pass as many Python scripts to the py_compile command as necessary.

    Copied! 
    python -m py_compile main.py another.py # or with python3 python3 -m py_compile main.py another.py 

    The command checks the syntax of the main.py and another.py files.

    The code for the main.py file:

    Copied! 
    if 10 > 5: print('bobbyhadz.com') 

    And the code for the another.py file:

    Copied! 
    if 5 == 5: print('google.com') 

    

    If I comment out the print() call in another.py :

    Copied! 
    if 5 == 5: # print('google.com') 

    Rerunning the command shows that the syntax error is caught.

    

    # Using the compileall command to check the syntax of all Python scripts in a directory

    If you need to check the syntax of all Python scripts in a directory, use the python -m compileall command.

    For example, to check the syntax of the Python scripts in the current directory, use the following command.

    Copied! 
    python -m compileall -q . # or python3 python3 -m compileall -q . 

    

    When the -q option is set, the list of files is not printed.

    Note that the command will also report syntax errors in files contained in subdirectories.

    For example, suppose we have an src directory that contains a file called another.py .

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    if 5 == 5: # print('google.com') 

    The file has a syntax error, so let’s try to rerun the compileall command.

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    python -m compileall -q . # or python3 python3 -m compileall -q . 

    

    You can also specify a directory when running the command.

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    python -m compileall -q src # or python3 python3 -m compileall -q src 

    The command compiles the files in a directory called src .

    # Using a custom Python script to check the syntax of other Python scripts

    You can also use a custom Python script to check the syntax of other Python scripts.

    Copied! 
    import sys file_names = sys.argv[1:] for file_name in file_names: source = open(file_name, 'r', encoding='utf8').read() + '\n' compile(source, file_name, 'exec') 

    Copied! 
    python check_syntax.py main.py # or with python3 python3 check_syntax.py main.py 

    Here is the example code for main.py .

    Copied! 
    if 10 > 5: print('bobbyhadz.com') 

    

    If I now change the code in main.py so it has a syntax error:

    Copied! 
    if 10 > 5: # print('bobbyhadz.com') 

    

    It catches the syntax error without running the file.

    You can also pass multiple files to the command.

    Here is the example code for another.py .

    Copied! 
    if 5 == 5: print('google.com') 

    Now let’s pass both files to the command.

    Copied! 
    python check_syntax.py main.py another.py # or with python3 python3 check_syntax.py main.py another.py 

    

    # Using the ast module to check the syntax of a Python script without running it

    You can also use the ast (Abstract Syntax Tree) module to check the syntax of a Python script without running it.

    Copied! 
    python -c "import ast; ast.parse(open('main.py').read())" # or with python3 python3 -c "import ast; ast.parse(open('main.py').read())" 

    Make sure to replace main.py with the name of your actual file.

    

    If there are no syntax errors in the file, the command produces no output.

    

    You can also define a custom Python script if you don’t want to use a command.

    Create a file called check_syntax.py and add the following code to it.

    Copied! 
    import ast import traceback file_name = 'main.py' with open(file_name, 'r', encoding='utf-8') as file: source = file.read() is_valid = True try: ast.parse(source) except SyntaxError: is_valid = False traceback.print_exc() print(f'Valid syntax: is_valid>') 

    Make sure to update the value of the file_name variable to specify the name of the file you want to check.

    Run the file with python check_syntax.py .

    Copied! 
    python check_syntax.py # or with python3 python3 check_syntax.py 

    

    If the file contains errors, they are printed to the terminal.

    

    # Check the syntax of a Python script using PyFlakes

    You can also use the PyFlakes module to check the syntax of a Python script without executing it.

    First, open your terminal and install the module.

    Copied! 
    pip install --upgrade pyflakes # or with pip3 pip3 install --upgrade pyflakes 

    Now use the module to check for syntax errors.

    Make sure to replace main.py with the name of your actual file.

    

    If the file doesn’t contain any errors, no output is printed.

    

    You can read more about using the PyFlakes module on the package’s GitHub page.

    The module checks Python source files for errors.

    The module works by parsing the source file, not by importing it.

    Therefore using the module with files that have side effects is safe.

    # Looking for a linter? Check out Pylint

    If you are looking for a linter, I’d recommend you check out Pylint.

    Pylint is a static code analyzer that analyses your code without actually running it.

    • checks for errors
    • enforces a coding standard
    • looks for code smells
    • makes suggestions on how the code should be refactored

    # Additional Resources

    You can learn more about the related topics by checking out the following tutorials:

    I wrote a book in which I share everything I know about how to become a better, more efficient programmer.

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