python学习6

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Python-字符串

双引号 “ “ 表string

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spam = "That is Alice's cat."
#out: That is Alice's cat.

转义字符

转义字符 打印为
```' 单引号
```" 双引号
\t 制表符
\n 换行符
``` \ 倒斜杠

e.g.

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print("Hello there!\nHow are you?\nI\'m doing fine.")
#Hello there!
#How are you?
#I'm doing fine.

开头加r，表示全部为字符串

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print(r'That is Carol\'s cat.')
#out:That is Carol\'s cat.

‘’’ ‘’’中加段落

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print('''Dear Alice, 

Eve's cat has been arrested for catnapping, cat burglary, and extortion. 

Sincerely, 

Bob''')

out：

Dear Alice,

Eve’s cat has been arrested for catnapping, cat burglary, and extortion.

Sincerely,

Bob

“”” “””中加注释：

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"""This is a test Python program. 

Written by Al Sweigart al@inventwithpython.com 

This program was designed for Python 3, not Python 2.  # annotation 

""" 

def spam(): 

"""This is a multiline comment to help 

explain what the spam() function does.""" 

print('Hello!')

下标与切片 Subscript and slice

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spam = 'Hello world!'
spam[0]
#out：'H' 
spam[4]
#out：'o' 
spam[-1]
#out：'!' 
spam[0:5] 
#out：'Hello' 
spam[:5] 
#out：'Hello' 
spam[6:]
#out：'world!'
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spam = 'Hello world!'
fizz = spam[0:5]
fizz
#out：'Hello'

in and not in

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'Hello' in 'Hello World'
#out:True 
'Hello' in 'Hello'
#out:True 
'HELLO' in 'Hello World'
#out:False 
'' in 'spam'
#out:True
'cats' not in 'cats and dogs'
#out:False

upper()、lower()、isupper()和 islower()

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spam = 'Hello world!'
spam = spam.upper()
spam
#out:'HELLO WORLD!' 
spam = spam.lower()
spam
#out:'hello world!'
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print('How are you?') 
feeling = input() 
if feeling.lower() == 'great': 
	print('I feel great too.') 
else: 
	print('I hope the rest of your day is good.')

out：

How are you?

GREat

I feel great too.

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spam = 'Hello world!'
spam.islower()
#out：False 
spam.isupper() 
#out：False 
'HELLO'.isupper()
#out：True 
'abc12345'.islower()
#out：True 
'12345'.islower()
#out：False 
'12345'.isupper()
#out：False
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'Hello'.upper()
#out：'HELLO' 
'Hello'.upper().lower()
#out：'hello' 
'Hello'.upper().lower().upper()
#out：'HELLO' 
'HELLO'.lower()
#out：'hello' 
'HELLO'.lower().islower()
#out：True

isX 字符串方法

  • isalpha()返回 True，如果字符串只包含字母，并且非空；

  • isalnum()返回 True，如果字符串只包含字母和数字，并且非空；

  • isdecimal()返回 True，如果字符串只包含数字字符，并且非空；

  • isspace()返回 True，如果字符串只包含空格、制表符和换行，并且非空；

  • istitle()返回 True，如果字符串仅包含以大写字母开头、后面都是小写字母的单词。

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'hello'.isalpha()
#out:True 
'hello123'.isalpha()
#out:False 
'hello123'.isalnum()
#out:True
'hello'.isalnum()
#out:True 
'123'.isdecimal()
#out:True 
' '.isspace()
#out:True 
'This Is Title Case'.istitle()
#out:True 
'This Is Title Case 123'.istitle()
#out:True 
'This Is not Title Case'.istitle()
#out:False 
'This Is NOT Title Case Either'.istitle()
#out:False

e.g.

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while True: 
	print('Enter your age:') 
	age = input() 
	if age.isdecimal(): 
		break 
	print('Please enter a number for your age.') 

while True: 
	print('Select a new password (letters and numbers only):') 
    password = input() 
    if password.isalnum(): 
        break 
    print('Passwords can only have letters and numbers.')

Enter your age:

forty two

Please enter a number for your age.

Enter your age:

42

Select a new password (letters and numbers only):

secr3t!

Passwords can only have letters and numbers.

Select a new password (letters and numbers only):

secr3t

startswith()和 endswith()

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'Hello world!'.startswith('Hello')
#out:True 
'Hello world!'.endswith('world!')
#out:True 
'abc123'.startswith('abcdef')
#out:False 
'abc123'.endswith('12')
#out:False 
'Hello world!'.startswith('Hello world!')
#out:True 
'Hello world!'.endswith('Hello world!')
#out:True

join()和 split()

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', '.join(['cats', 'rats', 'bats'])
'cats, rats, bats' 
' '.join(['My', 'name', 'is', 'Simon'])
'My name is Simon' 
'ABC'.join(['My', 'name', 'is', 'Simon'])
'MyABCnameABCisABCSimon'
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'My name is Simon'.split() #默认以空格分隔
#out：['My', 'name', 'is', 'Simon']
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'MyABCnameABCisABCSimon'.split('ABC')
#out：['My', 'name', 'is', 'Simon'] 
'My name is Simon'.split('m')
#out：['My na', 'e is Si', 'on']
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spam = '''Dear Alice,

How have you been? I am fine.

There is a container in the fridge

that is labeled "Milk Experiment".

Please do not drink it.

Sincerely,

Bob'''
spam.split('\n')
#out：['Dear Alice,', 'How have you been? I am fine.', 'There is a container in the #fridge', 'that is labeled "Milk Experiment".', '', 'Please do not drink it.', 
#'Sincerely,', 'Bob']

rjust()、ljust()和 center()

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'Hello'.rjust(10)
#out:'          Hello' 
'Hello'.rjust(20)
#out:'                    Hello' 
'Hello World'.rjust(20)
#out:'          Hello World' 
'Hello'.ljust(10)
#out:'Hello          '
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'Hello'.rjust(20, '\*')
#out:'***************Hello' 
'Hello'.ljust(20, '-')
#out:'Hello---------------'
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'Hello'.center(20)
#out:' Hello ' 
'Hello'.center(20, '=')
#out:'=======Hello========'
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def printPicnic(itemsDict, leftWidth, rightWidth): 
	print('PICNIC ITEMS'.center(leftWidth + rightWidth, '-')) 
	for k, v in itemsDict.items(): 
		print(k.ljust(leftWidth, '.') + str(v).rjust(rightWidth)) 

picnicItems = {'sandwiches': 4, 'apples': 12, 'cups': 4, 'cookies': 8000} 
printPicnic(picnicItems, 12, 5) 
printPicnic(picnicItems, 20, 6)

—PICNIC ITEMS–

sandwiches.. 4

apples…… 12

cups…….. 4

cookies….. 8000

——-PICNIC ITEMS——-

sandwiches………. 4

apples………….. 12

cups……………. 4

cookies…………. 8000

strip()、rstrip()和 lstrip()删除空白字符

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spam = ' Hello World '
spam.strip()
#out:'Hello World' 
spam.lstrip()
#out:'Hello World ' 
spam.rstrip()
#out:' Hello World'
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spam = 'SpamSpamBaconSpamEggsSpamSpam'
spam.strip('ampS')
#out:'BaconSpamEggs'