【Kaggle Learn】Python 5-8

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