python基础查漏补缺5--输入和输出

1. 字符转换格式

说  明  符	含  义
d	整数
o	八进制值
x	小写十六进制数
X	大写十六进制数
e	小写科学计数法表示的浮点数
E	大写科学计数法表示的浮点数
f	浮点数
s	字符串
%	%字符

>>> x = 0.01234567890123456789
>>> print('x = %f' % x)
x = 0.012346
>>> print('x = %e' % x)
x = 1.234568e-02
>>> print('x= %E' % x)
x= 1.234568E-02
>>> print('x = %o' % 100)
x = 144
>>> print('x = %x' % 100)
x = 64
>>> print('x = %x' % 200)
x = c8
>>> print('x = %X' % 200)
x = C8
>>> print('x = %s' % 'str')
x = str
>>> print('x = %d' % 200)
x = 200

　>>> print('x = %.2f' % x)
　x = 0.01

2. 格式字符串 format

>>> # 命名替换
>>> 'my {pet} has {prob}'.format(pet = 'dog', prob = 'fleas')
'my dog has fleas'
>>> # 位置替换
>>> 'my {0} has {1}'.format('dog', 'fleas')
'my dog has fleas'
>>> # 使用转换说明符
>>> '1/81 = {x}'.format(x = 1/81)
'1/81 = 0.012345679012345678'
>>> '1/81 = {x:f}'.format(x = 1/81)
'1/81 = 0.012346'
>>> '1/81 = {x:.2f}'.format(x = 1/81)
'1/81 = 0.01'
>>> # 使用大括号来指定格式设置参数
>>> 'num = {x:.{d}f}'.format(x = 1/81, d=4)
'num = 0.0123'
>>> # 格式化字符串更复杂一些，适合复杂任务，比如创建网页或者格式化邮件

3. 文件夹处理

函  数  名	作用
os.getcwd()	get current work directory 返回当前工作目录的名称
os.listdir(p)	list directory返回一个字符串列表，其中包含路径 p 指定的文件夹中所有文件和文件夹的名称
os.chdir(p)	change directory将当前工作目录设置为路径 p
os.path.isfile(p)	当路径 p 指定的是一个文件的名称时，返回 True，否则返回 False
os.path.isdir(p)	当路径 p 指定的是一个文件夹的名称时，返回 True，否则返回 False
os.stat(fname)	返回有关 fname 的信息，如大小（单位为字节）和最后一次修改时间
os.sep	返回当前操作系统的文件分隔符

>>> import os
>>> os.getcwd() 
'D:\dev\Python\practise\basic'
>>> cdir = os.getcwd()
>>> cdir
'D:\dev\Python\practise\basic'
>>> os.listdir(cdir)
['test_print.py', '__pycache__']
>>> os.chdir('D:\dev')
>>> os.getcwd()
'D:\dev'
>>> os.path.isfile('D:\dev\Python\practise\basic\test_print.py')
True
>>> os.path.isdir('D:\dev\Python\practise\basic\test_print.py')
False
>>> os.path.isdir('D:\dev\Python\practise\basic\')
True
>>> os.path.isdir('D:\dev\Python\practise\basic\test_print.py')
False
>>> os.stat('D:\dev\Python\practise\basic\test_print.py')
os.stat_result(st_mode=33206, st_ino=1688849860449070, st_dev=2025685481, st_nlink=1, st_uid=0, st_gid=0, st_size=137, st_atime=1505123394, st_mtime=1505125437, st_ctime=1505123394)

4. 文件读写

打开文件 --> 处理文件 --> 关闭文件

import os
def print_file(fname):
    # 打开文件，只读模式
    f = open(fname, 'r')
    # 按行读取文件内容
    for line in f:
        print(line, end='')
    # 关闭文件
    f.close()

def print_file2(fname):
    f = open(fname, 'r')
    # 读取文件全部内容
    print(f.read())
    # 关闭文件
    f.close()

def make_story1():
    # 如果文件已经存在的话，则不处理
    if os.path.isfile('story.txt'):
        print('story.txt is already exists')
    else:
        # 可写模式打开文件
        f = open('story.txt', 'w')
        # 写入文件内容
        f.write('Mary had a little lamb, 
')
        f.write('and then she had some more.
')

# 追加模式
def add_to_story(line, fname = 'story.txt'):
    f = open(fname, 'a')
    f.write(line)
    f.close()

# 字符串追加到文件开头
def insert_title(title, fname = 'story.txt'):
    f = open(fname, 'r+')
    temp = f.read()
    temp = title + '

' + temp
    f.seek(0) # 让文件指针指向文件夹
    f.write(temp)
make_story1()
add_to_story('and she had more and more')
insert_title('This is the title')
print_file('story.txt')
print_file2('story.txt')

result--------------
This is the title

Mary had a little lamb, 
and then she had some more.
and she had more and moreThis is the title

Mary had a little lamb, 
and then she had some more.
and she had more and more