目錄
1：查看內置函數及函數說明
Python3中有哪些內置函數呢？可以使用下面代碼查看：
print([item for item in dir(__builtins__) if not item.startswith('__') and item[0].islower() ])
"""
結果：
['abs', 'all', 'any', 'ascii', 'bin', 'bool', 'bytearray', 'bytes', 'callable', 'chr',
'classmethod', 'compile', 'complex', 'copyright', 'credits', 'delattr', 'dict', 'dir',
'divmod', 'enumerate', 'eval', 'exec', 'exit', 'filter', 'float', 'format', 'frozenset',
'getattr', 'globals', 'hasattr', 'hash', 'help', 'hex', 'id', 'input', 'int', 'isinstance',
'issubclass', 'iter', 'len', 'license', 'list', 'locals', 'map', 'max', 'memoryview',
'min', 'next', 'object', 'oct', 'open', 'ord', 'pow', 'print', 'property', 'quit', 'range',
'repr', 'reversed', 'round', 'set', 'setattr', 'slice', 'sorted', 'staticmethod', 'str',
'sum', 'super', 'tuple', 'type', 'vars', 'zip']
"""
如果不知道某個函數怎麼用，怎麼辦？ 使用help函數查看：
print(help(abs))
'''
abs(x, /)
Return the absolute value of the argument.
'''
print(help(all))
'''
all(iterable, /)
Return True if bool(x) is True for all values x in the iterable.
If the iterable is empty, return True.
'''
print(help(any))
'''
any(iterable, /)
Return True if bool(x) is True for any x in the iterable.
If the iterable is empty, return False.
'''
2：內置函數
2.1 map
print(help(map))
'''
class map(object)
| map(func, *iterables) --> map object
|
| Make an iterator that computes the function using arguments from
| each of the iterables. Stops when the shortest iterable is exhausted.
......
'''
意思就是把後面可迭代對象中每個元素傳遞給func處理：
lst1 = [1,2,3]
lst2 = [4,5,6]
# 一個參數，對應後面一個可以迭代對象
ret = list(map(lambda x: x **2,lst1))
print(ret) # [1, 4, 9]
# 兩個參數，對應後面兩個可以迭代對象
ret = list(map(lambda x,y:x+y + 10,lst1,lst2))
print(ret) # [15, 17, 19]
2.2 filter
print(help(filter))
'''
class filter(object)
| filter(function or None, iterable) --> filter object
|
| Return an iterator yielding those items of iterable for which function(item)
| is true. If function is None, return the items that are true.
......
'''
對後面可迭代對象中的每個元素，調用前面的函數處理，如果處理結果爲True，那麼這個元素會保留下來，否則會被過濾掉；
如果前面函數傳遞是None，那麼會把可迭代對象中爲真的值保留下來。
lst1 = [0,1,2,3,4,5,6,7,8,9]
def f(x):
return x % 3 == 0
# 使用普通函數
ret = list(filter(f,lst1))
print(ret) # [0, 3, 6, 9]
# 使用匿名函數
ret = list(filter(lambda x:x % 3 == 0,lst1))
print(ret) # [0, 3, 6, 9]
lst2 = [0,4,None,5,6,{},[1,2,3,0]]
ret = list(filter(None,lst2))
print(ret) # [4, 5, 6, [1, 2, 3, 0]] 只是作用於頂層元素
2.3 zip
print(help(zip))
"""
class zip(object)
| zip(iter1 [,iter2 [...]]) --> zip object
|
| Return a zip object whose .__next__() method returns a tuple where
| the i-th element comes from the i-th iterable argument. The .__next__()
| method continues until the shortest iterable in the argument sequence
| is exhausted and then it raises StopIteration.
......
|
"""
示例：
lst1 = [1,2,3]
lst2 = [4,5,6,14]
lst3 = [7,8,9,17,18]
z = zip(lst1,lst2,lst3)
print(list(z)) # 輸出: [(1, 4, 7), (2, 5, 8), (3, 6, 9)]
# 自己實現的zip
def myzip(*seqs):
seqs = [list(s) for s in seqs]
res = []
while all(seqs):
res.append( tuple(s.pop(0) for s in seqs ))
return res
lst1 = [1,2,3]
lst2 = [4,5,6,14]
lst3 = [7,8,9,17,18]
z = myzip(lst1,lst2,lst3)
print(list(z)) # [(1, 4, 7), (2, 5, 8), (3, 6, 9)]
2.4 sorted 排序
print(help(sorted))
"""
sorted(iterable, /, *, key=None, reverse=False)
Return a new list containing all items from the iterable in ascending order.
A custom key function can be supplied to customize the sort order, and the
reverse flag can be set to request the result in descending order.
"""
參數說明：
iterable：是可迭代類型;
key：傳入一個函數名，函數的參數是可迭代類型中的每一項，根據函數的返回值大小排序;
reverse：排序規則. reverse = True 降序 或者 reverse = False 升序，有默認值。
返回值：有序列表
lst = [3,1,44,5,11,90]
print(lst)
# 降序
lst2= sorted(lst,reverse = True)
print(lst2) # [90, 44, 11, 5, 3, 1]
# 升序(默認的)
lst2= sorted(lst)
print(lst2) # [1, 3, 5, 11, 44, 90]
lst = [3,1,44,-5,11,-90]
# 按照元素的絕對值來排序，降序
lst2= sorted(lst,key=abs,reverse = True)
print(lst2) # [-90, 44, 11, -5, 3, 1]
lst = [3,1,44,-5,11,-90]
# 使用匿名函數，降序
lst2= sorted(lst,key=lambda x:x if x >= 0 else -x,reverse = True)
print(lst2) # [-90, 44, 11, -5, 3, 1]