15-python_内建函数-string-list

水深无声 2022-09-17 06:29 137阅读 0赞

string处理  
\- 针对对象操作  
\- str.capitalize()  
\- str.replace()  
\- str.split()  
\- import string  
\- string.replace()  
list处理  
\- len()  
\- max()  
\- min()  
\- filter()  
\- zip()  
\- map()  
\- reduce()

# 1. str.capitalize() 首字母大写 #

capitalize(...)  
S.capitalize() -> string  
  
Return a copy of the string S with only its first character  
capitalized.  
>>>  
>>> "abc".capitalize()  
'Abc'

# 2. str.replace() 替换 #

replace(...)  
S.replace(old, new\[, count\]) -> string  
  
Return a copy of string S with all occurrences of substring  
old replaced by new. If the optional argument count is  
given, only the first count occurrences are replaced.  
>>>  
>>> "1999-09-19".replace("-", "/")  
'1999/09/19'  
>>> "1999-09-19".replace("-", "/", 1)  
'1999/09-19'

# 3. str.split() 分割,切割 #

split(...)  
S.split(\[sep \[,maxsplit\]\]) -> list of strings  
  
Return a list of the words in the string S, using sep as the  
delimiter string. If maxsplit is given, at most maxsplit  
splits are done. If sep is not specified or is None, any  
whitespace string is a separator and empty strings are removed  
from the result.  
>>>  
>>> "1999-09-19".split()  
\['1999-09-19'\]  
>>> "1999-09-19".split("-")  
\['1999', '09', '19'\]  
>>> "1999-09-19".split("-",1)  
\['1999', '09-19'\]

# 4. string.replace() #

>>> import string  
>>> help(string.replace)  
Help on function replace in module string:  
  
replace(s, old, new, maxreplace=-1)  
replace (str, old, new\[, maxreplace\]) -> string  
  
Return a copy of string str with all occurrences of substring  
old replaced by new. If the optional argument maxreplace is  
given, only the first maxreplace occurrences are replaced.  
>>>  
>>> string.replace("192.168.10.110", ".", "-")  
'192-168-10-110'

# 5. filter(), 保留符合条件的元素 #

filter(...)  
filter(function or None, sequence) -> list, tuple, or string  
  
Return those items of sequence for which function(item) is true. If  
function is None, return the items that are true. If sequence is a tuple  
or string, return the same type, else return a list.  
>>>  
>>> filter( lambda x: x > "1", "0123" )  
'23'  
>>> filter( lambda x: x > 1, ( 0, 1, 2, 3 ) )  
(2, 3)  
>>> filter( lambda x: x > 1, range(-1, 4) )  
\[2, 3\]

# 6. zip() 合并两个sequence #

zip(...)  
zip(seq1 \[, seq2 \[...\]\]) -> \[(seq1\[0\], seq2\[0\] ...), (...)\]  
  
Return a list of tuples, where each tuple contains the i-th element  
from each of the argument sequences. The returned list is truncated  
in length to the length of the shortest argument sequence.  
>>>  
>>> zip( (1, 2), (1, 2, 3) )  
\[(1, 1), (2, 2)\]  
>>> zip( \[1, 2, 3\], \[1, 2\] )  
\[(1, 1), (2, 2)\]

# 7. map() 将sequence转成list, #

map(...)  
map(function, sequence\[, sequence, ...\]) -> list  
  
Return a list of the results of applying the function to the items of  
the argument sequence(s). If more than one sequence is given, the  
function is called with an argument list consisting of the corresponding  
item of each sequence, substituting None for missing values when not all  
sequences have the same length. If the function is None, return a list of  
the items of the sequence (or a list of tuples if more than one sequence).  
>>>  
>>> map(None, \[1,2,3\], \['a', 'b'\])  
\[(1, 'a'), (2, 'b'), (3, None)\]  
>>> map(lambda x : x, "123")  
\['1', '2', '3'\]  
>>> map(lambda x,y : x+y, \[1,2,3\], \[10,20,30\])  
\[11, 22, 33\]

# 8. zip() 与 map() 的异同 #

\-当map中function为None时, map()的功能与zip()一致, 都是并行遍历.  
不同的是map()以最长的序列为准, 不足的补None,而zip()以最短的为准.  
\-当map中function不为None时, 会依次从各个sequence中取相同index的值做运算.

# 9. reduce() 依次取出每个item #

reduce(...)  
reduce(function, sequence\[, initial\]) -> value  
  
Apply a function of two arguments cumulatively to the items of a sequence,  
from left to right, so as to reduce the sequence to a single value.  
For example, reduce(lambda x, y: x+y, \[1, 2, 3, 4, 5\]) calculates  
((((1+2)+3)+4)+5). If initial is present, it is placed before the items  
of the sequence in the calculation, and serves as a default when the  
sequence is empty.  
>>>\# 4!  
>>> reduce(lambda x,y : x\*y, \[1, 2, 3, 4\])  
24  
>>>\# 1+2+...+99+100  
>>> reduce(lambda x,y : x+y, xrange(1, 101))  
5050