习题：
习题1:把一个文件中的所有数字删除
方式1:
#encoding=utf-8
content_list = []
with open("e:\\a.txt") as file_obj:
    for line in file_obj:
        for c in line:
            if c.isdigit():
                line=line.replace(c,"")
        content_list.append(line)
with open("e:\\a.txt","w") as fp:
    fp.writelines(content_list)

with open("e:\\a.txt") as fp:
    print(fp.read())

方式2:老师
filtered_content=""
with open("e:\\a.txt","r",encoding="utf-8") as fp:
    content=fp.read()
    for i in content:
        if i >="0" and i <= "9":
            continue
        else:
            filtered_content+=i

with open("e:\\a.txt","w",encoding="utf-8") as fp:
    fp.write(filtered_content)

with open("e:\\a.txt","r",encoding="utf-8") as fp:
    print(fp.read())

习题2把一个多级目录中所有文件的字母删除
方式1:
#encoding=utf-8

import os

for root,dirs,files in os.walk("d:\\test"):
    for file in files:
        os.chdir(root)
        with open(file,encoding="utf8") as file_obj:
            new_line_list = []

            for line in file_obj:
                for v in line:
                    if v.isalpha():
                        line = line.replace(v,"")
                new_line_list.append(line)
        os.chdir(root)
        with open(file,"w",encoding="utf8") as fp:
            fp.writelines(new_line_list)

方式2:老师:

import os.path
file_path=[]
for root,dirs,files in os.walk("e:\\letter"):
    for f in files:
        file_path.append(os.path.join(root,f))

print(file_path)

for file in file_path:
    filter_content = ""
    with open(file) as fp:
        content = fp.read()
        for letter in content:
            if (letter >="a" and letter <="z") \
               or (letter >="A" and letter <="Z"):
                continue
            else:
                filter_content+=letter
    with open(file,"w") as fp:
        fp.write(filter_content)

习题3：写函数或类，返回日期时间

当前的日期，格式："xxxx年xx月xx日"
当前的时间，格式："xx小时xx分钟xx秒"
当前的日期和时间，格式：xxxx年xx月xx日 xx小时xx分钟xx秒
把时间戳，转换为日期，格式："xxxx年xx月xx日"
把时间戳，转换为日期和时间，格式：xxxx年xx月xx日 xx小时xx分钟xx秒 

import time
class DateTime(object):
    def __init__(object):
        pass

    def current_date(self):
        localtime = time.localtime()
        year = str(localtime[0])
        month = str(localtime[1])
        day = str(localtime[2])
        return year + "年" + month + "月" + day + "日"

    def current_time(self):
        localtime = time.localtime()
        hour = str(localtime[3])
        min = str(localtime[4])
        sec = str(localtime[5])

        return hour +"时" + min + "分" + sec + "秒"

    def current_date_time(self):
        localtime = time.localtime()
        year = str(localtime[0])
        month = str(localtime[1])
        day = str(localtime[2])        
        localtime = time.localtime()
        hour = str(localtime[3])
        min = str(localtime[4])
        sec = str(localtime[5])
        return year + "年" + month + "月" + day + "日" + " " +  hour +"时" + min + "分" + sec + "秒"

    def from_timestamp_to_date(self,timestamp):
        localtime = time.localtime(timestamp)
        year = str(localtime[0])
        month = str(localtime[1])
        day = str(localtime[2])
        return year + "年" + month + "月" + day + "日"   

    def from_timestamp_to_time(self,timestamp):

        localtime = time.localtime(timestamp)
        year = str(localtime[0])
        month = str(localtime[1])
        day = str(localtime[2])        
        localtime = time.localtime()
        hour = str(localtime[3])
        min = str(localtime[4])
        sec = str(localtime[5])
        return year + "年" + month + "月" + day + "日" + " " +  hour +"时" + min + "分" + sec + "秒"         

if __name__ == "__main__":
    date_time = DateTime()
    print(date_time.current_date())
    print(date_time.current_time())
    print(date_time.current_date_time())
    print(date_time.from_timestamp_to_date(1254785455))
    print(date_time.from_timestamp_to_time(1254785455))

习题4:输入时间，计算距离1949年10月1日的天数

def is_leap_year(year):
    if (year%4==0 and year%100!=0) or year%400==0:
        return True
    else:
        return False

def count_days_interval():
    input_date=input(
"请输入日期，格式：year-month-day：")
    if input_date.count("-")!=2:
        print(
"输入日期格式有误，格式：year-month-day，请重新输入日期")
        return None
    year,month,day=input_date.split("-")
    if not (year.isdigit() and month.isdigit() and day.isdigit()):
        print(
"输入日期必须为数字，格式：year-month-day，请重新输入日期：")
    year=int(year)
    month=int(month)
    day=int(day)

    init_year = 1949
    init_month = 10
    init_day = 1

    if year-init_year==0:
        if month ==init_month:
            return day -init_day
        elif month -init_month==1:
            return 31+day-1
        else:
            return 31+30+day-1 
    elif year-init_year==1:
        month_days=[31,28,31,30,31,30,31,31,30,31,30,31]
        leap_day=0
        if month >2 and is_leap_year(year):
            leap_day=1
        days =0
        for i in month_days[:month-1]:
            days+=i
        return 92+leap_day+days+day
    else:
        month_days=[31,28,31,30,31,30,31,31,30,31,30,31]
        leap_day=0
        if month >2 and is_leap_year(year):
            leap_day=1
        days =0
        for i in month_days[:month-1]:
            days+=i
        leap_days=0
        for i in range(1950,year):
            if is_leap_year(i):
                leap_days+=1
        years = year -init_year-1
        return 92+leap_day+days+day+years*365+leap_days

print(count_days_interval())