Python Tutorial 笔记1

An Informal Introduction to Python

 

1. Number

 

>>> -7//3
-3
>>> 7//-3
-3
 

_ 表示最后的计算结果

 

2.  str

 

str是immutable的

 

word = "helloA"

word[1] # "e"

word[-1] #"A"

word[1:3] #"el"

word[3:1] #""

word[1:] #"elloA"

word[100] #exception

word[-100] #exception

len(word) #6

 

 

 

3.  Unicode

 "我的博客".encode("utf-8")

 4. List

 List和Str几乎一样，除了List是可以改变的。特别注意有些List的函数返回是None。

L=[1,2,3,4]
L=L.append(5) #none

 

 

More Control Flow Tools 

 

1. range()

 

 range(5) #0, 1, 2, 3, 4
 range(5, 10)   #5, 6, 7, 8, 9
 range(0, 10, 3) #0, 3, 6, 9
 range(-10, -100, -30) #-10, -40, -70

 

2.  定义函数

def fib(n):
  rst = []
  a, b = 0 ,1 
  while b < n:
    rst.append(b)
    a, b = b, a+b
  return rst

print(fib(1000))             

 如果一个函数没有return语句，那么这个函数返回None。

 3. 默认参数

def f(a, L=[]):
    L.append(a)
    return L

def g(a, L=None):
  if(L == None):
    L = []
  L.append(a)
  return L

print(f(1))  #[1]
print(f(2))  #[1,2]
print(f(3))  #[1,2,3]

print(g(1)) #[1]
print(g(2)) #[2]
print(g(3)) #[3]                 

   

4. Lambda

def getFun(n):
  return lambda x: x+n

f=getFun(10)
print(f(21)) #31            

Data Structures 

 

1. List

>>> a = [66.25, 333, 333, 1, 1234.5]
>>> print(a.count(333), a.count(66.25), a.count('x'))
2 1 0
>>> a.insert(2, -1)
>>> a.append(333)
>>> a
[66.25, 333, -1, 333, 1, 1234.5, 333]
>>> a.index(333)
1
>>> a.remove(333)
>>> a
[66.25, -1, 333, 1, 1234.5, 333]
>>> a.reverse()
>>> a
[333, 1234.5, 1, 333, -1, 66.25]
>>> a.sort()
>>> a
[-1, 1, 66.25, 333, 333, 1234.5]

 

  List comprehension

>>> vec = [2, 4, 6]
>>> [3*x for x in vec]
[6, 12, 18]

 

  Del

>>> a = [-1, 1, 66.25, 333, 333, 1234.5]
>>> del a[0]
>>> a
[1, 66.25, 333, 333, 1234.5]
>>> del a[2:4]
>>> a
[1, 66.25, 1234.5]
>>> del a[:]
>>> a
[]

 

 2. Tuple

>>> empty = ()
>>> singleton = 'hello',    # <-- note trailing comma
>>> len(empty)
0
>>> len(singleton)
1
>>> singleton
('hello',)

 

 3. Set

>>> basket = {'apple', 'orange', 'apple', 'pear', 'orange', 'banana'}
>>> print(basket)
{'orange', 'bananna', 'pear', 'apple'}
>>> fruit = ['apple', 'orange', 'apple', 'pear', 'orange', 'banana']
>>> fruit = set(basket)               # create a set without duplicates
>>> fruit
{'orange', 'pear', 'apple', 'banana'}
>>> fruit = {'orange', 'apple'}       # {} syntax is equivalent to [] for lists
>>> fruit
{'orange', 'apple'}
>>> 'orange' in fruit                 # fast membership testing
True
>>> 'crabgrass' in fruit
False

>>> # Demonstrate set operations on unique letters from two words
...
>>> a = set('abracadabra')
>>> b = set('alacazam')
>>> a                                  # unique letters in a
{'a', 'r', 'b', 'c', 'd'}
>>> a - b                              # letters in a but not in b
{'r', 'd', 'b'}
>>> a | b                              # letters in either a or b
{'a', 'c', 'r', 'd', 'b', 'm', 'z', 'l'}
>>> a & b                              # letters in both a and b
{'a', 'c'}
>>> a ^ b                              # letters in a or b but not both
{'r', 'd', 'b', 'm', 'z', 'l'}

 

 Set Comprehension

>>> a = {x for x in 'abracadabra' if x not in 'abc'}
>>> a
{'r', 'd'}

 

4. Dictionary

>>> tel = {'jack': 4098, 'sape': 4139}
>>> tel['guido'] = 4127
>>> tel
{'sape': 4139, 'guido': 4127, 'jack': 4098}
>>> tel['jack']
4098
>>> del tel['sape']
>>> tel['irv'] = 4127
>>> tel
{'guido': 4127, 'irv': 4127, 'jack': 4098}
>>> list(tel.keys())
['guido', 'irv', 'jack']
>>> 'guido' in tel
True
>>> 'jack' not in tel
False

 

Dictionary Comprehension

>>> {x: x**2 for x in (2, 4, 6)}
{2: 4, 4: 16, 6: 36}

 

 

5. Looping Techniques

>>> knights = {'gallahad': 'the pure', 'robin': 'the brave'}
>>> for k, v in knights.items():
...     print(k, v)
...
gallahad the pure
robin the brave

>>> for i, v in enumerate(['tic', 'tac', 'toe']):
...     print(i, v)
...
0 tic
1 tac
2 toe

>>> questions = ['name', 'quest', 'favorite color']
>>> answers = ['lancelot', 'the holy grail', 'blue']
>>> for q, a in zip(questions, answers):
...     print('What is your {0}?  It is {1}.'.format(q, a))
...
What is your name?  It is lancelot.
What is your quest?  It is the holy grail.
What is your favorite color?  It is blue.

>>> basket = ['apple', 'orange', 'apple', 'pear', 'orange', 'banana']
>>> for f in sorted(set(basket)):
...     print(f)
...
apple
banana
orange
pear

 

 

6.  More on Conditions

 

>>> string1, string2, string3 = '', 'Trondheim', 'Hammer Dance'
>>> non_null = string1 or string2 or string3
>>> non_null
'Trondheim'

 

7. Comparing Sequences and Other Types

 

(1, 2, 3)              < (1, 2, 4)
[1, 2, 3]              < [1, 2, 4]
'ABC' < 'C' < 'Pascal' < 'Python'
(1, 2, 3, 4)           < (1, 2, 4)
(1, 2)                 < (1, 2, -1)
(1, 2, 3)             == (1.0, 2.0, 3.0)
(1, 2, ('aa', 'ab'))   < (1, 2, ('abc', 'a'), 4)