input
input() function is used to get input from user (keyboard). input() allow user to input information to our program.
We can use a variable refer to the input message which is in fact a string.
your_name = input()
john
The friendly program should give the user some hints, prompting the user to enter certain information we want, such as name, age,etc
your_name = input("please input your name:")
your_age = input("please input your age:")
print("Hi,"+your_name+",your age is:"+your_age)
please input your name:john
please input your age:23
Hi,john,your age is:23
a= float(input("enter first number:"))
b= float(input("enter first number:"))
c= a+b
print("the sum of "+str(a)+" and "+str(b)+" is:"+str(c))
enter first number:2.3
enter first number:5.6
the sum of 2.3 and 5.6 is:7.8999999999999995
Explicit type conversion
We want to write a program to get the radius of a circle from the user and output the area of the circle.
r = input("pleanse enter the radius:")
pi = 3.1415916
area = 2*pi*r*r
print("the area of cieclr with radius "+r+"is:",area);
pleanse enter the radius:2.5
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-12-698e6bb5637b> in <module>
1 r = input("pleanse enter the radius:")
2 pi = 3.1415916
----> 3 area = 2*pi*r*r
4 print("the area of cieclr with radius "+r+"is:",area);
TypeError: can't multiply sequence by non-int of type 'float'
r is a string(character sequence),but pi is float type. they can do operator *
We should convert r from string type to float type.
r = input("pleanse enter the radius:")
r = float(r)
pi = 3.1415916
area = 2*pi*r*r
print("the area of cieclr with radius "+str(r)+"is:",area);
pleanse enter the radius:2.5
the area of cieclr with radius 2.5is: 39.269895
We use `float(r)` to convert r form str to float type, Later `str(r)` to to convert r form float to str type
We use type(variable) to convert variable from its original type to type type.
This is called explicit type conversion
To convert a binary string from a str type to an int type,we should pass 2 to the second parameter:
a = int("1011",2) # parameter represent it is binary str
print(a)
print(type(a))
11
<class 'int'>
To convert a hex string from a str type to an int type:
int('0x2d',16)
45
convert a int to str.
str(45)
'45'
bin(45)
'0b101101'
hex(45)
'0x2d'
oct(45)
'0o55'
convert a str to tuple:
tuple("hwdong")
('h', 'w', 'd', 'o', 'n', 'g')
list("hwdong")
['h', 'w', 'd', 'o', 'n', 'g']
t = (['a',1],['b',2],['c',3])
dict(t)
{'a': 1, 'b': 2, 'c': 3}
list(t)
[['a', 1], ['b', 2], ['c', 3]]
Implicit type conversion
Sometimes Python can automatically converts one data type to another data type. This process doesn’t need any user involvement.
When two data with different type involved in an operation.Implicit type conversion try to convert the lower data type (integer) to the higher data type (float) to avoid data loss. But this implicit type conversion may not be successful, for example, converting an int to a str.
a= 2
b =3.14
c = a+b
print(type(a+b))
print(type(c))
<class 'float'>
<class 'float'>
When two int values are divided, they are also automatically converted to float and divided again.
print(2/3)
type(2/3)
0.6666666666666666
float
If you want 2 int to do integer division, you can use the operator //
print(2//3)
type(2//3)
0
int
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