python学习记录（一）

1.打印操作

>>> print('hello')
hello
>>> print(1+2)
3

 

2.字符串操作

①

print(1+2+'3')
Traceback (most recent call last):
  File "<pyshell#2>", line 1, in <module>
    print(1+2+'3')
TypeError: unsupported operand type(s) for +: 'int' and 'str' #整数与字符串不能相加

②

>>> print('hello'*7)
hellohellohellohellohellohellohello #整数能与字符串相乘
>>> print('hello'*7.0)
Traceback (most recent call last):
  File "<pyshell#4>", line 1, in <module>
    print('hello'*7.0)
TypeError: can't multiply sequence by non-int of type 'float' #浮点数不能与字符串相乘

 

3.类型转化

①字符串转化为整数

>>> print(int("2") + int("3"))
5

②输入数据+类型转化+数据相加

>>> float(input("num1:"))+float(input("num2:"))
num1:30
num2:2
32.0

③关于报错

int(input("num1:"))
num1:2.0
Traceback (most recent call last):
  File "<pyshell#7>", line 1, in <module>
    int(input("num1:"))
ValueError: invalid literal for int() with base 10: '2.0' #输入为浮点数，与int不符

④例子

>>> float("210"*int(input("enter a number:")))
enter a number:2
210210.0 #210210转化为浮点型

 

4.变量

变量赋初值+变量的删除+输入变量值

>>> a=1
>>> print(a)
1
>>> print(a+3)
4
>>> print(a*2)
2
>>> a="hello"
>>> print(a*2)
hellohello
>>> del a
>>> print(a)
Traceback (most recent call last):
  File "<pyshell#20>", line 1, in <module>
    print(a)
NameError: name 'a' is not defined
>>> a = input("number:")
number:2
>>> print(a)
2

　　

5.赋值运算符

>>> a=1
>>> a+=2
>>> print(a)
3
>>> str1="abc"
>>> str1+="def"
>>> print(str1)
abcdef

与c语言相似，但无++等运算符

 

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