标签：sim rem time include nta title floor def cut
1.Numbers
a.The integer numbers (e.g. 2, 4, 20) have type int, the ones with a fractional part (e.g. 5.0, 1.6) have type float.
b.Division (/) always returns a float. To do floor division and get an integer result (discarding any fractional result) you can use the // operator; to calculate the remainder you can use %
c. use the ** operator to calculate powers
d. In interactive mode, the last printed expression is assigned to the variable _. for example:
>>> tax = 12.5 / 100
>>> price = 100.50
>>> price * tax
12.5625
>>> price + _
113.0625
>>> round(_, 2)
113.06
e. we can use Python for more complicated tasks than adding two and two together.
>>> # Fibonacci series:
... # the sum of two elements defines the next
... a, b = 0, 1
>>> while b < 10:
... print(b)
... a, b = b, a+b
...
1
1
2
3
5
8
2.Strings
a.Strings can be enclosed in single quotes (‘...‘) or double quotes ("...") with the same result.\can be used to escape quotes:
>>> ‘spam eggs‘ # single quotes
‘spam eggs‘
>>> ‘doesn\‘t‘ # use \‘ to escape the single quote...
"doesn‘t"
>>> "doesn‘t" # ...or use double quotes instead
"doesn‘t"
>>> ‘"Yes," he said.‘
‘"Yes," he said.‘
>>> "\"Yes,\" he said."
‘"Yes," he said.‘
>>> ‘"Isn\‘t," she said.‘
‘"Isn\‘t," she said.‘
b.The built-in function len() returns the length of a string:
c. Strings can be concatenated (glued together) with the + operator, and repeated with *:
>>> # 3 times ‘un‘, followed by ‘ium‘
>>> 3 * ‘un‘ + ‘ium‘
‘unununium‘
d. Two or more string literals (i.e. the ones enclosed between quotes) next to each other are automatically concatenated.
>>> ‘Py‘ ‘thon‘
‘Python‘
e. Strings can be indexed (subscripted), with the first character having index 0. There is no separate character type; a character is simply a string of size one:
>>> word = ‘Python‘
>>> word[0] # character in position 0
‘P‘
>>> word[5] # character in position 5
‘n‘
f. Indices may also be negative numbers, to start counting from the right,negative indices start from -1:
>>> word[-1] # last character ‘n‘ >>> word[-2] # second-last character ‘o‘ >>> word[-6] ‘P‘
g. In addition to indexing, slicing is also supported. While indexing is used to obtain individual characters, slicing allows you to obtain substring:
>>> word[0:2] # characters from position 0 (included) to 2 (excluded)
‘Py‘
>>> word[2:5] # characters from position 2 (included) to 5 (excluded)
‘tho‘
>>> word[:2] # character from the beginning to position 2 (excluded)
‘Py‘
>>> word[4:] # characters from position 4 (included) to the end
‘on‘
3.Lists
a. list, which can be written as a list of comma-separated values (items) between square brackets. Lists might contain items of different types, but usually the items all have the same type.
>>> squares = [1, 4, 9, 16, 25]
>>> squares
[1, 4, 9, 16, 25]
b. Like strings (and all other built-in sequence type), lists can be indexed and sliced:
>>> squares[0] # indexing returns the item
1
>>> squares[-1]
25
>>> squares[-3:] # slicing returns a new list
[9, 16, 25]
c. Unlike strings, which are immutable, lists are a mutable type, i.e. it is possible to change their content:
>>> cubes = [1, 8, 27, 65, 125] # something‘s wrong here
>>> 4 ** 3 # the cube of 4 is 64, not 65!
64
>>> cubes[3] = 64 # replace the wrong value
>>> cubes
[1, 8, 27, 64, 125]
d. You can also add new items at the end of the list, by using the append() method (we will see more about methods later):
>>> cubes.append(216) # add the cube of 6
>>> cubes.append(7 ** 3) # and the cube of 7
>>> cubes
[1, 8, 27, 64, 125, 216, 343]
e. It is possible to nest lists (create lists containing other lists), for example:
>>> a = [‘a‘, ‘b‘, ‘c‘]
>>> n = [1, 2, 3]
>>> x = [a, n]
>>> x
[[‘a‘, ‘b‘, ‘c‘], [1, 2, 3]]
>>> x[0]
[‘a‘, ‘b‘, ‘c‘]
>>> x[0][1]
‘b‘
参考：
标签：sim rem time include nta title floor def cut
原文地址：http://www.cnblogs.com/qlqiu/p/7742487.html
