PYTHON-错误-函数有返回值未接收导致替换不成功

#1.有返回值，没有赋值，替换不成功
cxj = 'guapi'
cxj.replace(cxj,'2b')
print(cxj)

#2.有返回值，赋值，替换成功
cxj = 'guapi'
cxj = cxj.replace(cxj,'2b')
print(cxj)