Python中eval函数的表达式作用示例

eval(expression[, globals[, locals]]) 

print(eval("123"))
print(eval("True"))
print(eval("(1,2,3)"))
print(eval("[1,2,3]")) 
# 输出结果
123
True
(1, 2, 3)
[1, 2, 3]

print(eval("1+2")) 
x = 1
print(eval('x+1'))
# 输出结果
3
2

a = 1
b = 2
print(eval("[a,b]")) 
# 输出结果
[1, 2]

# 使用 globals
x = 10
g = {"x": 5}
print(eval("x+1", g))
# 输出结果
6 

x = 10
y = 5
g = {"x": 5}
print(eval("x+1+y", g)) 
# 输出结果
5
    print(eval("x+1+y", g))
  File "<string>", line 1, in <module>
NameError: name 'y' is not defined

# 使用 locals
a = 1
g = {"a": 2, "b": 3}
l = {"b": 30, "c": 4} 
print(eval("a+b+c", g, l))
# 输出结果
36

# 字符串转字典
jsons = "{'a':123,'b':True}"
print(type(eval(jsons))) 
# 输出结果
<class 'dict'>

print(eval("{'name':'linux','age':age}", {"age": 123}))
# 输出结果
{'name': 'linux', 'age': 123}

print(eval("{'name':'linux','age':age}", {"age": 123}, {"age": 24})) 
# 输出结果
{'name': 'linux', 'age': 24}

# 内置函数
print(eval("dir()"))
print(eval("abs(-10)"))
  
# 输出结果
['__annotations__', '__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__', 'a', 'b', 'g', 'jsons', 'l', 'x', 'y']
10

print(eval("aa")) 
# 输出结果
    print(eval("aa"))
  File "<string>", line 1, in <module>
NameError: name 'aa' is not defined

print(eval("[a,b,c]"))
# 输出结果
    print(eval("[a,b,c]"))
  File "<string>", line 1, in <module>
NameError: name 'c' is not defined

print(eval("if x: print(x)"))
# 输出结果
    print(eval("if x: print(x)"))
  File "<string>", line 1
    if x: print(x)
    ^
SyntaxError: invalid syntax