简单了解python反射机制的一些知识

a = "12 + 43"
b = eval(a)
print(b)

a = "print(12 + 43); print(1111)"
b = eval(a)
print(b)
# 输出：
Traceback (most recent call last):
File "xxxx.py", line 10, in <module>
b = eval(a)
File "<string>", line 1
print(12 + 43); print(1111)
^
SyntaxError: invalid syntax

a = 1
b = eval("a = 21")
print(b)

b = exec("aa = 21")
print(b) # None，exec返回值为None
print(aa) # 21，exec执行了赋值语句，并定义了aa变量

a = '''ret = []
for i in range(10):
ret.append(i)'''
exec(a)
print(ret) # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

# 导入模块
exec("import config")
print(config.KEYWORD)
# 动态创建类
class Base:
def __init__(self):
print("Base")
a = "Base"
exec(a+"()")

class Base:
def __init__(self):
print("Base")
def test(self):
print("test")
return "Base::test"

b = eval("a.test()")
print(b)

test

Base::test

def hasattr(*args, **kwargs): # real signature unknown
"""
Return whether the object has an attribute with the given name.
This is done by calling getattr(obj, name) and catching AttributeError.
"""
pass

def has_attr(obj, name):
try:
eval("obj.%s()" % name)
return True
except AttributeError as e:
return False
a = Base()
if has_attr(a, "test"):
eval("a.test()")
# 输出：
Base
test
test

def getattr(object, name, default=None): # known special case of getattr
"""
getattr(object, name[, default]) -> value
Get a named attribute from an object; getattr(x, 'y') is equivalent to x.y.
When a default argument is given, it is returned when the attribute doesn't
exist; without it, an exception is raised in that case.
"""
pass

a = Base()
if hasattr(a, "test"):
func = getattr(a, "test")
func()
# 输出：
Base
test

def setattr(x, y, v): # real signature unknown; restored from __doc__
"""
Sets the named attribute on the given object to the specified value.
setattr(x, 'y', v) is equivalent to ``x.y = v''
"""
pass

class Base:
def __init__(self):
self.name = "name"
a = Base()
setattr(a, "name", "zhangsan")
print(a.name) # 改变原有属性的值
setattr(a, "age", 32)
print(getattr(a, "age")) # 新增不存在的属性，并设置值

def __import__(name, globals=None, locals=None, fromlist=(), level=0): # real signature unknown; restored from __doc__
"""
__import__(name, globals=None, locals=None, fromlist=(), level=0) -> module
Import a module. Because this function is meant for use by the Python
interpreter and not for general use, it is better to use
importlib.import_module() to programmatically import a module.
The globals argument is only used to determine the context;
they are not modified. The locals argument is unused. The fromlist
should be a list of names to emulate ``from name import ...'', or an
empty list to emulate ``import name''.
When importing a module from a package, note that __import__('A.B', ...)
returns package A when fromlist is empty, but its submodule B when
fromlist is not empty. The level argument is used to determine whether to
perform absolute or relative imports: 0 is absolute, while a positive number
is the number of parent directories to search relative to the current module.
"""
pass

a = __import__("config")
print(a.KEYWORD)

# function.py
def comm_function():
print("test_module")

a = __import__("comm.function")
a.comm_function()

Traceback (most recent call last):
File "xxx.py", line 10, in <module>
print(a.comm_function())
AttributeError: module 'comm' has no attribute 'comm_function'

a = __import__("comm.function", fromlist=True)
print(a.__name__)
a.comm_function()
# 输出：
comm.function
test_module