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Python Concepts for Data Science: The Eval and Exec Functions

Python's input function produces a string from the user's keyboard input. If we wish to treat that input as a number, we can use the int or float function to make the necessary conversion:

Here, whether the user enters 2 or 2.0, 'x' will be a variable with type floating point.

Please enter a number: 2
x =  2.0 type:  <class 'float'>

What if we wish 'x' to be of type integer if the user enters 2 and 'x' to be floating point if the user enters 2.0?

eval Function

Python's "__builtins__" module provides an function named eval that attempts to evaluate a string in the same way that the interactive shell would evaluate it.

when the user enters the text consisting of a single digit 10, the eval function interprets it as integer 10 and assigns an integer to the variable x1.

  1. when user enters a single digit 5, the eval function interprets it as integer 5 and assigns an integer to the variable x1

  2. When the user enters the text 5.0, the assigned variable is a floating-point variable.

  3. For x3, the user supplies the string "Python", and the variable’s type is string.

  4. When user enters x1. The eval function evaluates as a reference to the variable x1 which reference to the integer 5

  5. When user enters x6. the eval function treats x6 as a name and attempts to evaluate it. Since no variable named x6 exists, the eval function prints an error message

User could enter multiple entries separated by commas, and the eval function would evaluate the text typed by the user as Python tuple.

exec Function

The exec function, also from the __builtins__ module, is similar to the evel function. The exec function accepts a string parameter that consists of a Python source statement. The exec function interprets the statement and executes it.

When we execute the codes, the program will be looping until 'exit()' commit is entered.


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