What is the usage of eval in python

Usage of eval in python: Treat the string str as a valid expression to evaluate and return the calculation result. The syntax is [eval(source[, globals[, locals]]) -> value].

The operating environment of this tutorial: Windows 7 system, python version 3.9, DELL G3 computer. This method is suitable for all brands of computers.

Usage of eval in python:

Python eval() function function: evaluate the string str as a valid expression and return the calculation result.

Syntax:

eval(source[, globals[, locals]]) -> value

Parameters:

• source: a Python expression or code object returned by the function compile()

• globals: Optional. Must be dictionary

• locals: Optional. Any map object

If the globals parameter is provided, it must be of dictionary type; if the locals parameter is provided, it can be any map object.

Python's global namespace is stored in a dict object calledglobals(); the local namespace is stored in a dict object calledlocals(). We can use print (locals()) to view all variable names and variable values in the function body.

x = 1 y = 1 num = eval("x+y") print('num',num) def g(): x = 2 y = 2 num1 = eval("x+y") print('num1',num1) num2 =eval("x+y",globals()) print('num2',num2) num3 = eval("x+y",globals(),locals()) print('num3',num3) g() num 2 num1 4 num2 2 num3 4

Analysis: num2 is a global variable because it has globals, and the result after execution is 4; num3 has both globals and locals. In this case only, the value of locals is preferred, so the calculation result is 2

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