Python
contextlib
contextlib
利用__enter__和__exit__这两个方法实现上下文管理，就可以用with语句。
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| class Query(object):
def __init__(self, name):
self.name = name
def __enter__(self):
print('Begin')
return self
def __exit__(self, exc_type, exc_value, traceback):
if exc_type:
print('Error')
else:
print('End')
def query(self):
print('Query info about %s...' % self.name)
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| with Query('Bob') as q:
q.query()
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Python的标准库contextlib提供了更简单的写法。
@contextmanager这个decorator接受一个generator，yield语句生成的变量就是with ... as var中的变量。with语句首先执行yield之前的语句，yield调用会执行with语句内部的所有语句，最后执行yield之后的语句。
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| from contextlib import contextmanager
class Query(object):
def __init__(self, name):
self.name = name
def query(self):
print('Query info about %s...' % self.name)
@contextmanager
def create_query(name):
print('Begin')
q = Query(name)
yield q
print('End')
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| with create_query('Bob') as q:
q.query()
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| import contextlib
import time
@contextlib.contextmanager
def elapsed_timer(message):
start_time = time.time()
yield
LOGGER.info(message.format(time.time() - start_time))
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getattr
getattr
如果属性查找（attribute lookup）在实例以及对应的类中（通过__dict__)失败， 那么会调用到类的__getattr__函数, 如果没有定义这个函数，那么抛出AttributeError异常。
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| class StubLogger(object):
def __getattr__(self, name):
return self.log_print
def log_print(self, msg, *args):
print(msg % args)
LOGGER = StubLogger()
LOGGER.info("Hello %s!", "world")
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文件
读文件
读文件
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| with open('filename') as file:
for line in file:
do_things(line)
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写文件
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| with open('filename') as file:
file.write()
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路径拼接
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| os.path.join(path1, path2)
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String Split and Join
String Split and Join
In Python, a string can be split on a delimiter.
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| list = string.split(" ")
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Joining a string is simple:
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| string = "-".join(list)
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字典遍历
python字典遍历的几种方法
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| for key in dict:
for key in dict.keys():
for value in dict.values():
for key, value in dict.items():
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排列
python 全排列combinations和permutations函数
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| import itertools
s = [1, 2, 3]
print(list(itertools.combinations('abc', 2))) # [('a', 'b'), ('a', 'c'), ('b', 'c')]
print(list(itertools.permutations(s, 3))) # [(1, 2, 3), (1, 3, 2), (2, 1, 3), (2, 3, 1), (3, 1, 2), (3, 2, 1)]
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序列化
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| pickle.dump(variable, open('path.pkl', 'wb'))
variable = pickle.load(open('path.pkl', 'rb'))
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Pandas
遍历DataFrame
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| for index, row in df.iterrows():
row["column_name"]
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行选择
列选择
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| df.loc[:, ["column1", "column2"]]
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值选择
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| df.loc[df["column"] == value]
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loc和iloc的区别
https://stackoverflow.com/questions/31593201/how-are-iloc-and-loc-different
- loc gets rows (or columns) with particular labels from the index.
- iloc gets rows (or columns) at particular positions in the index (so it only takes integers).
取值
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| df.reset_index().at[0, "ndcg_at_10"]
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读取csv
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| action_data = pd.read_csv(data_path + 'Clothing_Shoes_and_Jewelry.csv', header=None, names=["user_id", "sku_id", "rating", "timestamp"])
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C++
argc & argv
Regarding main(int argc, char *argv[])
$ mysort 2 8 9 1 4 5
Argument Count, argc = 7
Argument Vector, argv[] = { “mysort”, “2”, “8”, “9”, “1”, “4”, “5” };
IDE
IDEA
- ctrl
- ctrl alt <-
- ctrl f12
- ctrl shift f
- shift shift
VSCode
- ctrl
- alt <-
- ctrl shift o
- shift alt f
