python使用数字与字符串方法技巧

def mark_trip_as_featured(trip):
    """将某个旅程添加到推荐栏目
    """
    if trip.source == 11:
        do_some_thing(trip)
    elif trip.source == 12:
        do_some_other_thing(trip)
    ... ...
    return

from enum import IntEnum

class TripSource(IntEnum):
    FROM_WEBSITE = 11
    FROM_iOS_CLIENT = 12


def mark_trip_as_featured(trip):
    if trip.source == TripSource.FROM_WEBSITE:
        do_some_thing(trip)
    elif trip.source == TripSource.FROM_ioS_CLIENT:
        do_some_other_thing(trip)
    ... ...
    return

def fetch_users(conn, min_level=None, gender=None, has_membership=False, sort_field="created"):
    """获取用户列表
   
    :param int min_level: 要求的最低用户级别，默认为所有级别
    :param int gender: 筛选用户性别，默认为所有性别
    :param int has_membership: 筛选所有会员/非会员用户，默认非会员
    :param str sort_field: 排序字段，默认为按 created "用户创建日期"
    :returns: 列表：[(User ID, User Name), ...]
    """
    # 一种古老的 sql 拼接技巧，使用 "WHERE 1=1" 来简化字符串拼接操作
    # 区分查询 params 来避免 SQL 注入问题
    statement = "SELECT id, name FROM users WHERE 1=1"
    params = []
    if min_level is not None:
        statement += " AND level >= ?"
        params.append(min_level)
    if gender is not None:
        statement += " AND gender >= ?"
        params.append(gender)
    if has_membership:
        statement += " AND has_membership == true"
    else:
        statement += " AND has_membership == false"
    
    statement += " ORDER BY ?"
    params.append(sort_field)
    return list(conn.execute(statement, params))

def fetch_users_v2(conn, min_level=None, gender=None, has_membership=False, sort_field="created"):
    """获取用户列表
    """
    query = select([users.c.id, users.c.name])
    if min_level is not None:
        query = query.where(users.c.level >= min_level)
    if gender is not None:
        query = query.where(users.c.gender == gender)
    query = query.where(users.c.has_membership == has_membership).order_by(users.c[sort_field])
    return list(conn.execute(query))

def f1(delta_seconds):
    # 如果时间已经过去了超过 11 天，不做任何事
    if delta_seconds > 950400:
        return 
    ...

def f1(delta_seconds):
    if delta_seconds < 11 * 24 * 3600:
        return

>>> True + 1
2
>>> 1 / False
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ZeroDivisionError: division by zero

>>> l = [1, 2, 4, 5, 7]
>>> sum(i % 2 == 0 for i in l)
2

# 类似的三元表达式："javascript" if 2 > 1 else "Python"
>>> ["Python", "Javascript"][2 > 1]
'Javascript'

s = (
    "There is something really bad happened during the process. "
    "Please contact your administrator."
)

from textwrap import dedent

def main():
    if user.is_active:
        # dedent 将会缩进掉整段文字最左边的空字符串
        message = dedent("""\
            Welcome, today's movie list:
            - Jaw (1975)
            - The Shining (1980)
            - Saw (2004)""")

>>> 10_000_000.0  # 以“千”为单位划分数字
10000000.0
>>> 0xCAFE_F00D  # 16进制数字同样有效，4个一组更易读
3405705229
>>> 0b_0011_1111_0100_1110  # 二进制也有效
16206
>>> int('0b_1111_0000', 2)  # 处理字符串的时候也会正确处理下划线
240

# A. 根据年龄升序排序，没有提供年龄放在最后边
>>> users = {"tom": 19, "jenny": 13, "jack": None, "andrew": 43}
>>> sorted(users.keys(), key=lambda user: users.get(user) or float('inf'))
['jenny', 'tom', 'andrew', 'jack']

# B. 作为循环初始值，简化第一次判断逻辑
>>> max_num = float('-inf')
>>> # 找到列表中最大的数字
>>> for i in [23, 71, 3, 21, 8]:
...:    if i > max_num:
...:         max_num = i
...:
>>> max_num
71

def incr(value):
    value += 1


# 使用 dis 模块查看字节码
import dis

dis.dis(incr)
      0 LOAD_FAST                0 (value)
      2 LOAD_CONST               1 (1)
      4 INPLACE_ADD
      6 STORE_FAST               0 (value)
      8 LOAD_CONST               0 (None)
     10 RETURN_VALUE