2.4 conversion of different data types

We often need to convert between different data types . Common conversions are centered on integers , Let's look at integers and three other types of conversions .

Let's first look at how to convert from floating-point numbers to integers . There are generally two basic transformations ： One is called rounding , That is, only the whole number of decimals is retained , Do not automatically round , You can use int Function .

num = 1.65
print(int(num))

Output is ：1. Of course , Rounding also has different forms , For example, you can also round up ,1.65 Rounding off 2. Then we need to use ceil function ,ceil It means ceiling , It's very figurative , That is, the smallest integer greater than the floating-point number .

import math
num = 1.05
print(math.ceil(num))

Output is ：2. This is the first time we use functions in other modules . stay Python in , In addition to various standard ready-made functions , We can also import other modules , Like here math modular （ Mathematical calculation module ）, Get more functions , The way to use it is to add the name of the import module before the function name .

however , What if I can't remember clearly or it's too troublesome to write ？ About how to be in PyCharm Auto import library , Here are PyCharm An important shortcut key for , namely “Alt+Enter”, If there is no import of necessary modules in the code , Can be in PyCharm Click... At the relevant code in the editing environment , And press this shortcut key , The system will prompt ：

choice “Import this name（ Import this name ）” You can further select the required module , Enter again to confirm , You can automatically complete the writing of the import statement .

The second is called rounding , have access to round Function ：

num = 1.65
print(round(num))

Output is ：2.

Let's look at a strange question ：

print(round(1.65, 1))
print(round(1.75, 1))

Output is ：
1.6
1.8

There's a detail to note here , Round to the nearest Python In the “ Round to the nearest pair ” The rules of , A more balanced carry design can be achieved , Five into pairs means that if the high order is singular, it will go forward 1, If the high order is an even number, there is no carry . So it produces the above effect .

Let's look at converting from integer to floating point number . This is simpler .

num = 2
print(float(num))

Output is ：2.0.

float Function can not only convert integers to floating-point numbers , For any other type that can be converted , For example, strings can also be converted ：

num = '3.14'
print(float(num))

Output is ：3.14.

In numerical calculation , Integers and floating-point numbers are often mixed , here Python By default, integers are automatically converted to floating-point numbers .

r = 2
pi = 3.14
print(r * r * pi)

Output is ：12.56, It can be used to express the calculation of circle area .

More precise pi You can use it directly math Modular pi Constant values ：

import math
r = 2
print(r * r * math.pi)

Output is ：12.566370614359172. The numerical accuracy of the output results is higher .

In fact, Boolean value is also an integer in storage , Fake is 0, True or false 0, Usually, the 1 Express . Let's watch two exercises ：

flag = 1 > 2
print(flag + 1)

Output is ：1.

num = 1
print(num + True)

Output is ：2.

so , Boolean and integer can indeed be mixed . Of course, we don't recommend that you do this , But in later code , When it comes to true or false judgment , Remember 0 It's fake . Indicates that the judgment conditions are not met , No 0 It means true , But the other way around , False correspondence 0, And truth only corresponds to 1.