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How to Check Syntax Errors in Python Code ?


In this post , we will explore - How to Check Syntax Errors in Python Code. You can use various options to check for any syntax errors in Python without executing the script . Try the below options -

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')
  • Next run your Python script(say yourPythonScript.py) against the above script


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 :

  • You can use PyChecker to syntax check your python code. Use code below from the command line:


    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
 

  • If you want to syntax check multiple Python scripts at one go ,


pychecker <YOUR\_DIR>/\*.py
Sample how pychecker shows the syntax errors -



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 :

  • Another worthy option to try - https://github.com/PyCQA/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())"
  • Check syntax of any block of code


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=\[\]))\])"
  • Alternatively use as a python script


import ast, traceback

g = '<YOUR PYTHON SCRIPT NAME>'
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)
Hope this write up was helpful.  

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