1. sum() 二维元组降维，本质就是多个元组也能相加。
>>> tpl = ( (1,2,3),(1,2) ) >>> sum(tpl,()) (1, 2, 3, 1, 2) >>> sum(tpl,(0,)) (0, 1, 2, 3, 1, 2) >>> tpl = ( (1,2,3),(4,5) ) >>> sum(tpl,()) (1, 2, 3, 4, 5) >>> sum(tpl,(0,)) # 单元素元组要加逗号：(0,)，否则 (0)==0 (0, 1, 2, 3, 4, 5) >>> (1,2,3)+(4,5) (1, 2, 3, 4, 5) >>> (0,)+(1,2,3)+(4,5) (0, 1, 2, 3, 4, 5) >>>
【实例】编写函数，接收数列，返回一个元组，其中第一个元素为所有参数的平均值，其他元素为所有参数中大于平均值的实数。
以下两个函数等价：
def func1(lst): t = sum(lst)/len(lst) return sum((tuple(i for i in lst if i>t),),(t,)) def func2(lst): t = sum(lst)/len(lst) return (t,)+tuple(i for i in lst if i>t)
相关阅读：上期第2点列表降维：Python 在问答频道中刷题积累到的小技巧（二）_Hann Yang的博客-CSDN博客
2. '#'号输出日期短格式：'%Y-%#m-%#d' => '2022-6-6'。
附datetime.date常用属性及方法：
>>> import datetime as dt >>> d = dt.date(2022,6,6) >>> d.year 2022 >>> d.month 6 >>> d.day 6 >>> d.weekday() 0 >>> d.isoweekday() 1 >>> d.max datetime.date(9999, 12, 31) >>> d.min datetime.date(1, 1, 1) >>> d.ctime() 'Mon Jun 6 00:00:00 2022' >>> d.timetuple() time.struct_time(tm_year=2022, tm_mon=6, tm_mday=6, tm_hour=0, tm_min=0, tm_sec=0, tm_wday=0, tm_yday=157, tm_isdst=-1) >>> d.strftime('%Y-%#m-%#d') #日期短格式 '2022-6-6' >>> d.isoformat() '2022-06-06' >>> d.isocalendar() (2022, 23, 1) #当年第23周第1天 >>> d.resolution datetime.timedelta(days=1) >>> d + dt.timedelta(2) datetime.date(2022, 6, 8) >>> d.toordinal() 738312 >>> d-d.min datetime.timedelta(days=738311) >>> d - dt.timedelta(d.toordinal()-1) datetime.date(1, 1, 1) >>> d.max-d datetime.timedelta(days=2913747) >>> dt.date(2023,1,1)-d datetime.timedelta(days=209) datetime.date(2022, 6, 6) >>> d.replace(2023) datetime.date(2023, 6, 6) >>> d.replace(d.year,7) datetime.date(2022, 7, 6) >>> d.replace(d.year,d.month,8) datetime.date(2022, 6, 8) >>> d.replace(d.year,7,8) datetime.date(2022, 7, 8) >>> d.replace(2002,7,8) datetime.date(2002, 7, 8) >>> d datetime.date(2022, 6, 6) #d未变更
3. 列表指定位置插入、替换或删除元素：lst[m:m] = [x] 。
>>> lst = [1,2,3,4,5] >>> lst [1, 2, 3, 4, 5] >>> lst[3:3] = [0] >>> lst [1, 2, 3, 0, 4, 5] >>> lst[3] = [0] # 对比 >>> lst [1, 2, 3, [0], 4, 5] >>> lst[3:4] = [] # 删除索引为3的元素 >>> lst [1, 2, 3, 4, 5] >>> lst[3:3] = [] # 这样lst没有变动 >>> lst [1, 2, 3, 4, 5] >>> lst[3:3] = [6,7,8] >>> lst [1, 2, 3, 6, 7, 8, 4, 5] >>> lst[3:6] = [] # 恢复原状 >>> lst [1, 2, 3, 4, 5] >>> lst[-1:] = [7,8,9] # 列表去尾相接 >>> lst [1, 2, 3, 4, 7, 8, 9] >>> lst[4:] = [5] # 恢复原状 >>> lst [1, 2, 3, 4, 5] >>> lst[1:4] = [0, 0, 0] # 替换 >>> lst [1, 0, 0, 0, 5] >>> lst[2:3] = [1, 1] # 替换+插入 >>> lst [1, 0, 1, 1, 0, 5] >>> lst.insert(3, 2) # 单个元素插入等价于 lst[3:3]=[2] >>> lst [1, 0, 1, 2, 1, 0, 5] >>> >>> lst = [*range(1,6)] >>> lst[-1:] = range(1,6)[::-1] >>> lst [1, 2, 3, 4, 5, 4, 3, 2, 1] >>> lst[:4] = [] # 删除前面的字符 >>> lst [5, 4, 3, 2, 1]
4. 多项式求和时循环变量设置成题目中的一致，只要照抄。
例1： 2/(1*3) - 3/(2*5) + 4/(3*7) - 5/(4*9) + ... + (-1)^(n-1) * (n+1) / [ n*(2*n+1) ]
m = int(input()) s = 0 for n in range(1,m+1): s += (-1)**(n-1) * (n+1) / ( n*(2*n+1) ) print(round(s, 4))
例2： 1 - 1/2! + 1/4! - 1/6! + ... + (-1)^(n-1)/(2n-2)!
m = int(input()) res, t = 1.0, 1 for n in range(1,m): t *= (2*n - 1) * n*2 //最后一项是(n-1),代入n*2即(2*n-2) res += (-1)**n/t print(res)
5. 任意多个递增序列合并一个递增序列（非相加后排序）。
L0 = [3, 21, 24, 30, 36, 43, 46, 71, 82, 84, 96] L1 = [7, 15, 22, 23, 32, 39, 41, 51, 74, 76, 87, 89] L2 = [1, 18, 27, 31, 34, 35, 37, 48, 53, 57, 58, 81, 85, 97, 100] L = [list(i) for i in (L0, L1, L2)] res = [] while sum(map(lambda x:len(x),L)): t, dic = [], {} for i in range(len(L)): if L[i]: dic[L[i][0]] = i t.append(L[i][0]) res.append(min(t)) L[dic[min(t)]][:1] = [] print(res)
附录：
Help on class date in module datetime: class date(builtins.object) | date(year, month, day) --> date object | | Methods defined here: | | __add__(self, value, /) | Return self+value. | | __eq__(self, value, /) | Return self==value. | | __format__(...) | Formats self with strftime. | | __ge__(self, value, /) | Return self>=value. | | __getattribute__(self, name, /) | Return getattr(self, name). | | __gt__(self, value, /) | Return self>value. | | __hash__(self, /) | Return hash(self). | | __le__(self, value, /) | Return self<=value. | | __lt__(self, value, /) | Return self<value. | | __ne__(self, value, /) | Return self!=value. | | __radd__(self, value, /) | Return value+self. | | __reduce__(...) | __reduce__() -> (cls, state) | | __repr__(self, /) | Return repr(self). | | __rsub__(self, value, /) | Return value-self. | | __str__(self, /) | Return str(self). | | __sub__(self, value, /) | Return self-value. | | ctime(...) | Return ctime() style string. | | isocalendar(...) | Return a 3-tuple containing ISO year, week number, and weekday. | | isoformat(...) | Return string in ISO 8601 format, YYYY-MM-DD. | | isoweekday(...) | Return the day of the week represented by the date. | Monday == 1 ... Sunday == 7 | | replace(...) | Return date with new specified fields. | | strftime(...) | format -> strftime() style string. | | timetuple(...) | Return time tuple, compatible with time.localtime(). | | toordinal(...) | Return proleptic Gregorian ordinal. January 1 of year 1 is day 1. | | weekday(...) | Return the day of the week represented by the date. | Monday == 0 ... Sunday == 6 | | ---------------------------------------------------------------------- | Class methods defined here: | | fromisocalendar(...) from builtins.type | int, int, int -> Construct a date from the ISO year, week number and weekday. | | This is the inverse of the date.isocalendar() function | | fromisoformat(...) from builtins.type | str -> Construct a date from the output of date.isoformat() | | fromordinal(...) from builtins.type | int -> date corresponding to a proleptic Gregorian ordinal. | | fromtimestamp(timestamp, /) from builtins.type | Create a date from a POSIX timestamp. | | The timestamp is a number, e.g. created via time.time(), that is interpreted | as local time. | | today(...) from builtins.type | Current date or datetime: same as self.__class__.fromtimestamp(time.time()). | | ---------------------------------------------------------------------- | Static methods defined here: | | __new__(*args, **kwargs) from builtins.type | Create and return a new object. See help(type) for accurate signature. | | ---------------------------------------------------------------------- | Data descriptors defined here: | | day | | month | | year | | ---------------------------------------------------------------------- | Data and other attributes defined here: | | max = datetime.date(9999, 12, 31) | | min = datetime.date(1, 1, 1) | | resolution = datetime.timedelta(days=1)
