What does eval mean in python

eval is a built-in function in python. The basic syntax is "eval(expression, globals=None, locals=None)". Its usage is: 1. Evaluate simple mathematical expressions; 2. eval Variables defined in the global namespace will be used during the evaluation process; 3. Multiple lines of Python code can be encapsulated in a string and executed with eval, and the results can be accessed in the global namespace.

The operating environment of this article: Windows 10 system, python version 3.11.2, dell g3 computer.

eval is a built-in function in Python that is used to parse and execute strings as code. Its basic syntax is eval(expression, globals=None, locals=None), where expression is a string that evaluates expressions, and globals and locals are optional parameters used to specify global and local namespaces.

The function of eval is to evaluate a Python expression represented in string form and return the result of the expression.

The following is the usage of eval:

1. Evaluate simple mathematical expressions

result = eval('2 + 2')
print(result) # 输出4

2. Use variables

x = 5
y = 10
result = eval('x + y')
print(result) # 输出15

As you can see, eval will use variables defined in the global namespace during the evaluation process.

3. Execute Python code block

code = '''
def multiply(a, b):
return a * b
result = multiply(2, 3)
'''
eval(code)
print(result) # 输出6

You can encapsulate multiple lines of Python code in a string and execute it with eval. The result can be accessed in the global namespace arrive.

It should be noted that eval has the ability to execute arbitrary code, so pay attention to security issues when using eval and avoid executing code from untrusted code.

Summary

eval in Python is a function used to execute expressions and code blocks in the form of strings. Its flexibility allows you to convert strings into executable Python codes. For some flexible calculation and code execution needs, eval can provide a convenient and concise solution. However, due to its ability to execute arbitrary code, it must be used with caution to avoid security issues.

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