【Kaggle Learn】Python 5-8

ゝ一纸荒年。 2022-03-17 12:10 113阅读 0赞

# 五. Booleans and Conditionals #

> Using booleans for branching logic

x = True
    print(x)
    print(type(x))
    
    ''' True <class 'bool'> '''

①Booleans  
Python has a type bool which can take on one of two values: True and False.

②Comparison Operations  
a == b, and, or, not等等

Python的逻辑运算返回值(或运算结果)为布尔代数形式

3.0 == 3
    True
    
    '3' == 3
    False

①Python provides operators to combine boolean values using the standard concepts of “and”, “or”, and “not”.

def can_run_for_president(age, is_natural_born_citizen):
        """Can someone of the given age and citizenship status run for president in the US?"""
        # The US Constitution says you must be a natural born citizen *and* at least 35 years old
        return is_natural_born_citizen and (age >= 35)
    
    print(can_run_for_president(19, True))
    print(can_run_for_president(55, False))
    print(can_run_for_president(55, True))
    """ The result is: False False True """

②"and", “or”, and "not"有运算优先级  
not>and>or  
【为了防止记错可以用括号】

True or True and False
    """ The result is: True """

③当逻辑关系比较复杂时,可以分层写

prepared_for_weather = have_umbrella or ((rain_level < 5) and have_hood) or (not (rain_level > 0 and is_workday))
    
    prepared_for_weather = (
        have_umbrella 
        or ((rain_level < 5) and have_hood) 
        or (not (rain_level > 0 and is_workday))
    )

Conditionals(条件语句)  
if, **elif(新)**, and else.  
**【记得加冒号 : 以及加缩进】**  
除了else, 其他有判断条件

*Note especially the use of colons ( : ) and whitespace to denote separate blocks of code. This is similar to what happens when we define a function - the function header ends with :, and the following line is indented with 4 spaces. All subsequent indented lines belong to the body of the function, until we encounter an unindented line, ending the function definition.*

def inspect(x):
        if x == 0:
            print(x, "is zero")
        elif x > 0:
            print(x, "is positive")
        elif x < 0:
            print(x, "is negative")
        else:
            print(x, "is unlike anything I've ever seen...")
    
    inspect(0)
    inspect(-15)
    """ The result is: 0 is zero -15 is negative """

之前有int(), float()  
现在有Boolean conversion bool()

print(bool(1)) # all numbers are treated as true, except 0
    print(bool(0))
    print(bool("asf")) # all strings are treated as true, except the empty string ""
    print(bool(""))
    # Generally empty sequences (strings, lists, and other types we've yet to see like lists and tuples)
    # are "falsey" and the rest are "truthy"
    """ True False True False """

if else语句两种写法

def quiz_message(grade):
        if grade < 50:
            outcome = 'failed'
        else:
            outcome = 'passed'
        print('You', outcome, 'the quiz with a grade of', grade)
    
    
    def quiz_message(grade):
        outcome = 'failed' if grade < 50 else 'passed'
        #逻辑运算outcome = ('failed' if grade < 50 else 'passed')
        #相当于c语言中的outcome = grade < 50 ? 'failed' : 'passed'
        print('You', outcome, 'the quiz with a grade of', grade)

# 六. Exercise: Booleans and Conditionals #

略

# 七. Lists #

> Lists and the things you can do with them. Includes indexing, slicing and mutating

类似复合的数组,可以有数字,字符串,甚至函数等

my_favourite_things = [32, 'raindrops on roses', help]
    
    my_favourite_things[0]
    #和数组一样 从0数起
    32
    
    my_favourite_things[2]
    #Type help() for interactive help, or help(object) for help about object.
    
    my_favourite_things[-1]
    #Type help() for interactive help, or help(object) for help about object.
    #数组序号可用负数, -1即为离0最远的元素, -2即为次远

二维数组两种写法

hands = [
        ['J', 'Q', 'K'],
        ['2', '2', '2'],
        ['6', 'A', 'K'], # (Comma after the last element is optional)
    ]
    # (I could also have written this on one line, but it can get hard to read)
    hands = [['J', 'Q', 'K'], ['2', '2', '2'], ['6', 'A', 'K']]

Slicing 跟matlab中一样, 求得数组的某行某列至某行某列  
此处的冒号 : 即有 “到” 的意思

planets = ['Mercury', 'Venus', 'Earth', 'Mars', 'Jupiter', 'Saturn', 'Uranus', 'Neptune']
    
    planets[0:3]
    ['Mercury', 'Venus', 'Earth']
    
    planets[:3]
    ['Mercury', 'Venus', 'Earth']
    #planets[0:3] is our way of asking for the elements of planets starting from index 0 
    #and continuing up to but not including index 3.可以理解为左闭右开[m,n)
    
    planets[3:]
    ['Mars', 'Jupiter', 'Saturn', 'Uranus', 'Neptune']
    
    # The last 3 planets
    planets[-3:]
    ['Saturn', 'Uranus', 'Neptune']

# 八. Exercise: Lists #