How to Execute a String Containing Code in Python

In this quick tutorial, we'll show how to execute string containing Python code in Python and Jupyter.

In other words we will run Python code dynamically from another Python code. We'll first look into executing code with statements, then code with expressions, and finally we will cover Jupyter Notebooks.

Step 1: Execute a String statements in Python

We can use method exec to execute statement stored as a string in Python code.

Below we can find simple example of executing string as code in Python with exec():

some_code = 'print ("Hello World!")'
exec(some_code)

The result is printing the:

Hello World!

More information about method exec() can be found in the official documentation: exec - Built-in Functions

The method is described as:

This function supports dynamic execution of Python code. object must be either a string or a code object. If it is a string, the string is parsed as a suite of Python statements which is then executed (unless a syntax error occurs).

The parameters of the method exec:

• object - Either a string or a code object
• globals (optional) - a dictionary
• locals (optional)- a mapping object

The parameters globals and locals allow a user to specify what global and local functions / variables are available.

Step 2: Execute a String expression in Python

To execute strings containing Python expressions we can use method - eval. Method eval takes string containing expression and evaluate it as Python code:

x = 1
eval('x+1')

result:

2

The official documentation can be found on this link: eval - Built-in Functions.

The method is described as:

The expression argument is parsed and evaluated as a Python expression (technically speaking, a condition list) using the globals and locals dictionaries as global and local namespace.

Step 3: Execute a String code in Jupyter Notebook

If you need to execute dynamically Python code which is evaluated from a string in Jupyter Notebook we can use the same methods:

• exec
• eval

Both can read code from another file or Jupyter Notebook and execute it:

x = 1
eval('x+1')

result:

2

Step 4: Execute a Multiline String code in Python

Finally let's see how we can execute multiline string as a Python code with method exec in simple example:

some_code = """
x = 0
if x == False :
    print("x Is False")
else :
    print("x Is True")
"""
exec(some_code)

the result is printed on the Python console:

x Is False

Conclusion

In this article, we looked at different solutions for executing and evaluating string expressions or statements as Python code.

We focused on executing in these code examples, but evaluating is very similar and simpler.