python学习_14
exec（str） 可以执行多行语句，语句块，没有返回值
command = """ ... a= [1,2,3] ... for i in a: ... print(i) ... """ exec(command) 1 2 3 a = [1,2,3] for i in a: ... exec("print(" + str(i) + ")") ... 1 2 3
eval(str) 只能执行单行语句，有返回值
a = eval("2*4") a 8 s = "print(" + str(10) + ")" eval(s) 10
函数引用 函数名可以赋值给其他的变量引用，用引用加括号可以直接调用原函数
a = abs a(-10) 10 def func(f): ... print(f(-1)) ... func(abs) 1
函数解包传递参数 解包元组传参
def func(args): ... print(args) ... t = (2,3,4) func(t) #可以利用星号加上元组名传递参数 (2, 3, 4) def add(a,b):return a+b ... add(*(1,2)) 3
解包字典传参
def func(kwargs): ... for k,v in kwargs.items(): ... print(k,v) ... d = {"name":"huhongqiang","age":18,"sex":"m"} func(d) name huhongqiang age 18 sex m def sub(a,b): ... return a - b ... sub(**{"a":3,"b":2}) 1
习题8：[1,2,3,4,5] 变成 [2,3,4,5,1] 方法1：
a=[1,2,3,4,5]
result = []
result.append(a[-1])
result.extend(a[0:4])
print(result)方法2：
result = []
result.append(a[-1])
for v in a[0:4]:
result.append(v)
print(result)方法3：
a=[1,2,3,4,5]
result = []
for v in a[0:4]:
result.append(v)
result.insert(0,a[-1])
print(result)习题9：统计字符串的个数
l = [1,2,"s",[1,23],{1:2},(1,2),set([1,2]),"b"]
str_number = 0
for v in l:
if isinstance(v,str):
str_number += 1
print(str_number)习题10:统计列表中所有类型数据的个数
l = [1,2,"s",[1,23],{1:2},(1,2),set([1,2]),"b"]
d = {"str":0,"list":0,"tuple":0,"int":0,"set":0}
for v in l:
if isinstance(v,str):
d["str"] += 1
elif isinstance(v,list):
d["list"] += 1
elif isinstance(v,tuple):
d["tuple"] += 1
elif isinstance(v,set):
d["set"] += 1
#elif isinstance(v,int):
#d["int"] += 1
print(d)习题11：求列表中所有数字的和，包括数字字符串
a = [1,2,3,[4,5,6],{1:6,2:8,"a":"12",3:4}]
result = 0
for value in a:
if isinstance(value,int):
result += value
elif isinstance(value,list):
for v in value:
if isinstance(v,int):
result += v
elif isinstance(value,dict):
for key in value.keys():
if isinstance(key,int):
result += key
for v in value.values():
if isinstance(v,int):
result += v
elif v.isdigit():
result += int(v)
print(result)a = [1,2,3,[4,5,6],{1:6,2:8,"a":"12",3:4}] 这个地方有个小坑，判断字典value值是否是数字的时候，要先把判断int的放在前面，否则会报错；
result = 0
for value in a:
if isinstance(value,int):
result += value
elif isinstance(value,list):
for v in value:
if isinstance(v,int):
result += v
elif isinstance(value,dict):
for key in value.keys():
if isinstance(key,int):
result += key
for v in value.values():
#这个先判断了是否是数字字符串，因为整数没有isdigit()方法
if v.isdigit():
result += v
elif isinstance(v,int):
result += int(v)
print(result) 腾讯云开发者
