精品--百日python，路线：语法->爬虫->网站->数据科学->机器学习->深.zip

# Python-100-Days-CheatSheet 百日python，路线：语法->爬虫->网站->数据科学->机器学习->深度学习 ## Day 01：语法 python原生封装的数据结构，按`增删改查`组织 列表 ---- ```python <list> = <list>[from_inclusive : to_exclusive : step_size] <list>.append(<el>) <list>.extend(<collection>) <list> += [<el>] <list> += <collection> ``` ```python <list>.sort() <list>.reverse() <list> = sorted(<collection>) <iter> = reversed(<list>) ``` ```python sum_of_elements = sum(<collection>) elementwise_sum = [sum(pair) for pair in zip(list_a, list_b)] sorted_by_second = sorted(<collection>, key=lambda el: el[1]) sorted_by_both = sorted(<collection>, key=lambda el: (el[1], el[0])) flattened_list = list(itertools.chain.from_iterable(<list>)) list_of_chars = list(<str>) product_of_elems = functools.reduce(lambda out, x: out * x, <collection>) no_duplicates = list(dict.fromkeys(<list>)) ``` ```python index = <list>.index(<el>) # 返回第一个匹配 <el> 的索引 <list>.insert(index, <el>) # 在 index 处插入为 <el>，右边元素右移 <el> = <list>.pop([index]) # 移除 index 处的 <el> ，默认移除列表的最后一个元素 <list>.remove(<el>) # 移除第一次出现的 <el> <list>.clear() # 移除所有 ``` 字典 ---------- ```python <view> = <dict>.keys() <view> = <dict>.values() <view> = <dict>.items() ``` ```python value = <dict>.get(key, default) # key 不存在则返回 default 默认值 value = <dict>.setdefault(key, default) # 同上，同时给 dict 指定对应 key 的 default 默认值 <dict> = collections.defaultdict(<type>) # 创建一个字典，值的默认类型为 <type> <dict> = collections.defaultdict(lambda: 1) # 创建一个字典，默认值为 1 ``` ```python <dict>.update(<dict>) # 或: dict_a = {**dict_a, **dict_b}. <dict> = dict(<list>) # 用键值对列表初始化一个字典 <dict> = dict(zip(keys, values)) # 用两个列表初始化一个字典 <dict> = dict.fromkeys(keys [, value]) # 用键列表初始化一个字典 ``` ```python value = <dict>.pop(key) # 移除 key，返回被移除的值 {k: v for k, v in <dict>.items() if k in keys} # 按多个 key 过滤字典 ``` ### Counter 计数器 ```python >>> from collections import Counter >>> colors = ['blue', 'red', 'blue', 'yellow', 'blue', 'red'] >>> counter = Counter(colors) Counter({'blue': 3, 'red': 2, 'yellow': 1}) >>> counter.most_common()[0][0] 'blue' ``` Set --- ```python <set> = set() <set>.add(<el>) <set>.update(<collection>) <set> |= {<el>} <set> |= <set> ``` ```python <set> = <set>.union(<coll.>) # 或: <set> | <set> <set> = <set>.intersection(<coll.>) # 或: <set> & <set> <set> = <set>.difference(<coll.>) # 或: <set> - <set> <set> = <set>.symmetric_difference(<coll.>) # 或: <set> ^ <set> <bool> = <set>.issubset(<coll.>) # 或: <set> <= <set> <bool> = <set>.issuperset(<coll.>) # 或: <set> >= <set> ``` ```python <set>.remove(<el>) # 有错误会抛出. <set>.discard(<el>) # 不会抛出错误 ``` ### Frozenset #### 是否可作为字典的键 ```python <frozenset> = frozenset(<collection>) ``` Range ----- ```python range(to_exclusive) range(from_inclusive, to_exclusive) range(from_inclusive, to_exclusive, step_size) range(from_inclusive, to_exclusive, -step_size) ``` ```python from_inclusive = <range>.start to_exclusive = <range>.stop ``` Enumerate --------- ```python for i, el in enumerate(<collection> [, i_start]): ... ``` 自定义名字的元组 ----------- ```python >>> Point = collections.namedtuple('Point', 'x y') >>> p = Point(1, y=2) Point(x=1, y=2) >>> p[0] 1 >>> p.x 1 >>> getattr(p, 'y') 2 >>> p._fields # 或: Point._fields ('x', 'y') ``` Iterator -------- ```python <iter> = iter(<collection>) <iter> = iter(<function>, to_exclusive) ``` #### 读取输入，空行停止 ```python for line in iter(input, ''): ... ``` #### 同上，每次在输入前加一条信息，不计入读取的输入 ```python from functools import partial for line in iter(partial(input, 'Please enter value: '), ''): ... ``` ### Next **返回下一个元素。 如果没下一个元素了，抛出错误或返回 default** ```python <el> = next(<iter> [, default]) ``` #### Skips first item: ```python next(<iter>) for element in <iter>: ... ``` Generator --------- **方便实现迭代协议** ```python def step(start, step_size): while True: yield start start += step_size ``` ```python >>> stepper = step(10, 2) >>> next(stepper), next(stepper), next(stepper) (10, 12, 14) ``` Type ---- ```python <type> = type(<el>) # <class 'int'> / <class 'str'> / ... ``` ```python from numbers import Number, Integral, Real, Rational, Complex <bool> = isinstance(<el>, Number) ``` ```python <bool> = callable(<el>) ``` String ------ ```python <str> = <str>.strip() # 移除 <str> 首尾两边的空白字符 <str> = <str>.strip('<chars>') # 移除 <str> 首尾两边由 <chars> 指定的字符 ``` ```python <list> = <str>.split() # 按空格字符切分成列表 <list> = <str>.split(sep=None, maxsplit=-1) # 按 'sep' 字符串切分成列表，至多 'maxsplit' 次. <str> = <str>.join(<list>) # 以 <str> 为分隔符合并 <list> 的所有元素. ``` ```python <str> = <str>.replace(old_str, new_str) <bool> = <str>.startswith(<sub_str>) # 可以传字符串元组 <bool> = <str>.endswith(<sub_str>) # 可以传字符串元组 <int> = <str>.index(<sub_str>) # 返回子串的第一个索引 <bool> = <str>.isnumeric() # <str> 含数字则返回 True <list> = textwrap.wrap(<str>, width) # 漂亮地将字符串折叠成行 ``` ### Char ```python <str> = chr(<int>) # int 转换成 unicode <int> = ord(<str>) # unicode 转换成 int. ``` ```python >>> ord('0'), ord('9') (48, 57) >>> ord('A'), ord('Z') (65, 90) >>> ord('a'), ord('z') (97, 122) ``` Regex ----- ```python import re <str> = re.sub(<regex>, new, text, count=0) # 替换所有 <list> = re.findall(<regex>, text) # 返回所有匹配的字符串 <list> = re.split(<regex>, text, maxsplit=0) # 按正则表达式来切缝字符串 <Match> = re.search(<regex>, text) # 找第一次出现正则表达式匹配的 <Match> = re.match(<regex>, text) # 只在 text 的开始找 <iter> = re.finditer(<regex>, text) # 返回所有匹配的对象，是个迭代器 ``` * **参数 `'flags=re.IGNORECASE'` 可以和所有函数一起使用.** * **参数 `'flags=re.DOTALL'` 让点也匹配行.** * **使用 `r'\1'` 或 `'\\\\1'` 匹配退格符.** * **使用 `'?'` 实现非贪心.** ### Match Object ```python <str> = <Match>.group() # Whole match. <str> = <Match>.group(1) # Part in first bracket. <tuple> = <Match>.groups() # All bracketed parts. <int> = <Match>.start() # <Match> 的头索引 <int> = <Match>.end() # <Match> 的尾索引 ``` ### Special Sequences **Use capital letter for negation.** ```python '\d' == '[0-9]' # 匹配数字 '\s' == '[ \t\n\r\f\v]' # 匹配空白字符 '\w' == '[a-zA-Z0-9_]' # 匹配字母表 ``` 字符串格式化 ------ ```python <str> = f'{<el_1>}, {<el_2>}' <str> = '{}, {}'.format(<el_1>, <el_2>) ``` ```python >>> Person = namedtuple('Person', 'name height') >>> person = Person('Jean-Luc', 187) >>> f'{person.height:10}' ' 187' >>> '{p.height:10}'.format(p=person) ' 187' ``` ### 基本操作 ```python {<el>:<10}