数据类型

>>> 2+2
4
>>> # 这是注释
... 2+2
4
>>> 2+2  # 代码同一行的注释
4
>>> (50-5*6)/4
5.0
>>> 8/5 # 整数相除时并不会丢失小数部分
1.6

>>> 3 * 3.75 / 1.5
7.5
>>> 7.0 / 2
3.5

>>> import decimal
>>> a = decimal.Decimal(9876)                       # 可以接受整数或字符串作为参数
>>> b = decimal.Decimal("54321.012345678987654321") # 小数必须用字符串！
>>> a + b
Decimal('64197.012345678987654321')

>>> import fractions
>>> x = fractions.Fraction(1, 3)
>>> x
Fraction(1, 3)
>>> x * 2
Fraction(2, 3)
>>> y = fractions.Fraction(6, 4)
>>> y
Fraction(3, 2)
>>> x == 1 / (2 * y)
True
>>> fractions.Fraction(0, 0)
Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "/usr/lib/python3.3/fractions.py", line 167, in __new_
_
    raise ZeroDivisionError('Fraction(%s, 0)' % numerator)
ZeroDivisionError: Fraction(0, 0)
>>> 

>>> 1j * 1J
(-1+0j)
>>> 1j * complex(0, 1)
(-1+0j)
>>> 3+1j*3
(3+3j)
>>> (3+1j)*3
(9+3j)
>>> (1+2j)/(1+1j)
(1.5+0.5j)

>>> a=1.5+0.5j
>>> a.real
1.5
>>> a.imag
0.5

#!/usr/bin/Python
# Filename: str_format.py
age = 25
name = 'Swaroop'
print('{0} is {1} years old'.format(name, age))
print('Why is {0} playing with that Python?'.format(name))

>>> s = "The sword of truth"
>>> "{0}".format(s)  # default formatting
"The sword of truth"
>>> "{0:25}".format(s)  # minimum width 25
'The sword of truth       '
>>> "{0:>25}".format(s)  # right align, minimum width 25
'       The sword of truth'
>>> "{0:^25}".format(s)  # center align, minimum width 25
'   The sword of truth    '
>>> "{0:-^25}".format(s)  # - fill, center align, minimum width 25
'---The sword of truth----'
>>> "{0:.<25}".format(s)  # . fill, left align, minimum width 25
'The sword of truth.......'
>>> "{0:.10}".format(s)  # maximum width 10
'The sword '

>>> "{0:b} {0:o} {0:x} {0:X}".format(14613198)
'110111101111101011001110 67575316 deface DEFACE'
>>> "{0:#b} {0:#o} {0:#x} {0:#X}".format(14613198)
'0b110111101111101011001110 0o67575316 0xdeface 0XDEFACE'

>>> "{0:,}{0:*>13,}".format(int(2.39432185e6))
'2,394,321****2,394,321'

>>> by = b'abcd\x65'
>>> by 
b'abcde'
>>> type(by) 
<class 'bytes'> 
>>> len(by)
5 
>>> by += b'\xff' 
>>> by 
b'abcde\xff' 
>>> len(by) 
6 
>>> by[0] 
97 
>>> by[0] = 102 # 错误：字节和字符串一样都是不可变类型
Traceback (most recent call last): 
  File "<stdin>", line 1, in <module> 
TypeError: 'bytes' object does not support item 
assignment 

>>> by = b'abcd\x65' 
>>> barr = bytearray(by)
>>> barr 
bytearray(b'abcde') 
>>> len(barr)
5 
>>> barr[0] = 102 
>>> barr 
bytearray(b'fbcde') 

>>> by = b'd' 
>>> s = 'abcde' 
>>> by + s
Traceback (most recent call last): 
  File "<stdin>", line 1, in <module> 
TypeError: can't concat bytes to str
>>> s.count(by) 
Traceback (most recent call last): 
  File "<stdin>", line 1, in <module> 
TypeError: Can't convert 'bytes' object to str 
implicitly 
>>> s.count(by.decode('ascii'))
1 

>>> a_string = '深入 Python'
>>> len(a_string) 
9 
>>> by = a_string.encode('utf‐8')
>>> by 
b'\xe6\xb7\xb1\xe5\x85\xa5 Python' 
>>> len(by) 
13 
>>> by = a_string.encode('gb18030')
>>> by 
b'\xc9\xee\xc8\xeb Python' 
>>> len(by) 
11 
>>> by = a_string.encode('big5')
>>> by 
b'\xb2`\xa4J Python' 
>>> len(by) 
11 
>>> roundtrip = by.decode('big5')
>>> roundtrip 
'深入 Python' 
>>> a_string == roundtrip 
True 

>>> int("45")
45
>>> type(45)
<class 'int'>
>>> str("92")
'92'
>>> type('92')
<class 'str'>

>>> type(None) 
<class 'NoneType'> 
>>> None == False 
False 
>>> None == 0 
False 
>>> None == '' 
False 
>>> None == None 
True 
>>> x = None 
>>> x == None 
True 
>>> y = None 
>>> x == y 
True 

#!/usr/bin/python
# Filename: using_list.py
# This is my shopping list

shoplist = ['apple', 'mango', 'carrot', 'banana']
print('I have', len(shoplist), 'items to purchase.')
print('These items are:', end=' ')
for item in shoplist:
    print(item, end=' ')
    
print('\nI also have to buy rice.')
shoplist.append('rice')
print('My shopping list is now', shoplist)

print('I will sort my list now')
shoplist.sort()
print('Sorted shopping list is', shoplist)

print('The first item I will buy is', shoplist[0])
olditem = shoplist[0]
del shoplist[0]
print('I bought the', olditem)
print('My shopping list is now', shoplist)

#!/usr/bin/python
# Filename: using_tuple.py

zoo = ('python', 'elephant', 'penguin') # 注意小括号是可选的
print('Number of animals in the zoo is', len(zoo))

new_zoo = ('monkey', 'camel', zoo)
print('Number of cages in the new zoo is', len(new_zoo))
print('All animals in new zoo are', new_zoo)
print('Animals brought from old zoo are', new_zoo[2])
print('Last animal brought from old zoo is', new_zoo[2][2])
print('Number of animals in the new zoo is',

len(new_zoo)-1+len(new_zoo[2]))

>>> (MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, 
SATURDAY, SUNDAY) = range(7) 
>>> MONDAY
0
>>> TUESDAY
1
>>> SUNDAY 
6

>>> a = 5; b = 8
>>> a, b = b, a
>>> a, b
(8, 5)

>>> def get_error_details():
...     return (2, 'second error details')
...
>>> errnum, errstr = get_error_details()
>>> errnum
2
>>> errstr
'second error details'

>>> a, *b = [1, 2, 3, 4]
>>> a
1
>>> b
[2, 3, 4]

d = {key1:value1, key2:value2}

d = dict(key1=value1, key2=value2)

#!/usr/bin/python
# Filename: using_dict.py

# 'ab'是'a'ddress'b'ook的缩写
ab = {  'Swaroop'   : 'swaroop@swaroopch.com',
        'Larry'     : 'larry@wall.org',
        'Matsumoto' : 'matz@ruby-lang.org',
        'Spammer'   : 'spammer@hotmail.com'
    }


print("Swaroop's address is", ab['Swaroop'])

# 删除一个键值对
del ab['Spammer']
print('\nThere are {0} contacts in the address-book\n'.format(len(ab)))
for name, address in ab.items():
    print('Contact {0} at {1}'.format(name, address))

# 修改一个键值对
ab['Larry'] = 'larry@larry.org'

# 添加一个键值对，和修改键值对完全一样
ab['Guido'] = 'guido@python.org'

# 查找某个键值对
if 'Guido' in ab: # 或者写成 ab.has_key('Guido')
    print("\nGuido's address is", ab['Guido'])

#!/usr/bin/python
# Filename: seq.py

shoplist = ['apple', 'mango', 'carrot', 'banana']
name = 'swaroop'

# Indexing or 'Subscription' operation
print('Item 0 is', shoplist[0])
print('Item 1 is', shoplist[1])
print('Item 2 is', shoplist[2])
print('Item 3 is', shoplist[3])
print('Item -1 is', shoplist[-1])
print('Item -2 is', shoplist[-2])
print('Character 0 is', name[0])

# Slicing on a list
print('Item 1 to 3 is', shoplist[1:3])
print('Item 2 to end is', shoplist[2:])
print('Item 1 to -1 is', shoplist[1:-1])
print('Item start to end is', shoplist[:]) # 全切片

# Slicing on a string
print('characters 1 to 3 is', name[1:3])
print('characters 2 to end is', name[2:])
print('characters 1 to -1 is', name[1:-1])
print('characters start to end is', name[:])

>>> shoplist = ['apple', 'mango', 'carrot', 'banana']
>>> shoplist[::1]
['apple', 'mango', 'carrot', 'banana']
>>> shoplist[::2]
['apple', 'carrot']
>>> shoplist[::3]
['apple', 'banana']
>>> shoplist[::-1]
['banana', 'carrot', 'mango', 'apple']

>>> a_set = {1}
>>> a_set
{1}
>>> type(a_set)
<class 'set'>
>>> a_set = {1, 2}
>>> a_set
{1, 2}
>>> {1, 2}
{1, 2}

>>> a_list = ['brazil', 'russia', 'india', 'russia']
>>> bri = set(a_list)
>>> bri
{'brazil', 'russia', 'india'}
>>> 'india' in bri
True
>>> 'usa' in bri
False
>>> bric = bri.copy()
>>> bric.add('china')
>>> bric.issuperset(bri)
True
>>> bri.remove('russia')
>>> bri & bric # OR bri.intersection(bric)
{'brazil', 'india'}

#!/usr/bin/python
# Filename: list_comprehension.py

listone = [2, 3, 4]
listtwo = [2*i for i in listone if i > 2]
print(listtwo)

>>> import os, glob 
>>> glob.glob('*.xml') 
['feed‐broken.xml', 'feed‐ns0.xml', 'feed.xml'] 
>>> [os.path.realpath(f) for f in glob.glob('*.xml')]
['c:\\Users\\pilgrim\\diveintopython3\\examples\\feed‐broken.xml', 
'c:\\Users\\pilgrim\\diveintopython3\\examples\\feed‐ns0.xml', 
'c:\\Users\\pilgrim\\diveintopython3\\examples\\feed.xml'] 

>>> import os, glob 
>>> metadata = [(f, os.stat(f)) for f in glob.glob('*test*.py')]
>>> metadata[0]
('alphameticstest.py', nt.stat_result(st_mode=33206, 
st_ino=0, st_dev=0, st_nlink=0, st_uid=0, st_gid=0, st_size=2509, 
st_atime=1247520344, st_mtime=1247520344, st_ctime=1247520344)) 
>>> metadata_dict = {f:os.stat(f) for f in glob.glob('*test*.py')} # 字典解析
>>> type(metadata_dict) 
<class 'dict'> 
>>> list(metadata_dict.keys()) 
['romantest8.py', 'pluraltest1.py', 'pluraltest2.py', 
'pluraltest5.py', 
'pluraltest6.py', 'romantest7.py', 'romantest10.py', 
'romantest4.py', 
'romantest9.py', 'pluraltest3.py', 'romantest1.py', 
'romantest2.py', 
'romantest3.py', 'romantest5.py', 'romantest6.py', 
'alphameticstest.py', 
'pluraltest4.py'] 
>>> metadata_dict['alphameticstest.py'].st_size 
2509 

>>> a_dict = {'a': 1, 'b': 2, 'c': 3} 
>>> {value:key for key, value in a_dict.items()} 
{1: 'a', 2: 'b', 3: 'c'} 

>>> a_set = set(range(10)) 
>>> a_set 
{0, 1, 2, 3, 4, 5, 6, 7, 8, 9} 
>>> {x ** 2 for x in a_set}
{0, 1, 4, 81, 64, 9, 16, 49, 25, 36} 
>>> {x for x in a_set if x % 2 == 0}
{0, 8, 2, 4, 6} 
>>> {2**x for x in range(10)}
{32, 1, 2, 4, 8, 64, 128, 256, 16, 512} 

>>> list(range(3, 6))            # 使用分离的参数正常调用
[3, 4, 5]
>>> list(range([3, 6]))          # 直接使用一个列表作为range()函数的参数会出错
Traceback (most recent call last):
  File "<input>", line 1, in <module>
TypeError: 'list' object cannot be interpreted as an integer
>>> args = [3, 6]
>>> list(range(*args))           # 通过解包列表参数调用
[3, 4, 5]

>>> def parrot(voltage, state='a stiff', action='voom'):
...     print("-- This parrot wouldn't", action, end=' ')
...     print("if you put", voltage, "volts through it.", end=' ')
...     print("E's", state, "!")
...
>>> d = {"voltage": "four million", "state": "bleedin' demised", "action": "VOOM"}
>>> parrot(**d)
-- This parrot wouldn't VOOM if you put four million volts through it. E's bleedin' demised !

>>> element = "Silver"
>>> number = 47
>>> "Element {number} is {element}".format(**locals())
'Element 47 is Silver'

#!/usr/bin/python
# Filename: str_methods.py

name = 'Swaroop' # 这是一个字符串对象
if name.startswith('Swa'):
    print('Yes, the string starts with "Swa"')
if 'a' in name:
    print('Yes, it contains the string "a"')
if name.find('war') != -1:
    print('Yes, it contains the string "war"')
delimiter = '_*_'
mylist = ['Brazil', 'Russia', 'India', 'China']
print(delimiter.join(mylist))