Python讀書筆記006：I/O
阿新 • • 發佈：2019-02-20
設定字串格式：
1、字串插入
>>> x=1/81
>>> x
0.012345679012345678
>>> print('value: %.2f' % x)
value: 0.01
>>> print('value: %.5f' % x)
value: 0.01235轉換說明符：
x=1/81 >>> print(x) 0.012345679012345678 >>> 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 = %d' % x) x = 0
>>> a, b, c = 'cat', 3.14, 6
>>> s = 'There\'s %d %s older than %.2f years' % (c, a, b)
>>> s
"There's 6 cat older than 3.14 years"
>>> s = 'There\'s %d %ss older than %.2f years' % (c, a, b)
>>> s
"There's 6 cats older than 3.14 years"2、格式字串
>>> 'My {pet} has {prob}'.format(pet='dog',prob='fleas') 'My dog has fleas' >>> 'My {0} has {1}'.format('dog','flea') 'My dog has flea' >>> '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:.3f}'.format(x=1/81) '1/81=0.012'
>>> 'num={x:.{d}f}'.format(x=1/81,d=3)
'num=0.012'
>>> 'num={x:.3f}'.format(x=1/81)
'num=0.012'
>>> 'num={x:.{c}f}'.format(x=1/81,c=5)
'num=0.01235'
>>> 'num={x:.5f}'.format(x=1/81)
'num=0.01235'檢查檔案和資料夾
獲悉當前工作目錄中的檔案和資料夾：
>>> import os >>> os.listdir(os.getcwd()) ['DLLs', 'Doc', 'include', 'Lib', 'libs', 'LICENSE.txt', 'NEWS.txt', 'python.exe', 'python3.dll', 'python36.dll', 'pythonw.exe', 'Scripts', 'tcl', 'test.png', 'Tools', 'vcruntime140.dll']
處理文字檔案
逐行讀取文字檔案：
def print_file(fname):
f=open(fname,'r')
for line in f:
print(line,end='')
f.close()
>>> print_file('e:\\Python\\data.txt')
apple
banana
car
pear
Tencent Technology Company Limiteddef print_file(fname):
f=open(fname,'r')
for line in f:
print(line)
f.close()
>>> print_file('e:\\Python\\data.txt')
apple
banana
car
pear
Tencent Technology Company Limited因為檔案中各行都是以\n結尾的。
將整個文字檔案作為一個字串進行讀取：
def print_file2(fname):
f=open(fname,'r')
print(f.read())
f.close()
>>> print_file2('e:/Python/data.txt')
apple
banana
car
pear
Tencent Technology Company Limited>>> fname='e:/Python/data.txt'
>>> print(open(fname,'r').read())
apple
banana
car
pear
Tencent Technology Company Limited寫入文字檔案：
def make_story1():
f=open('story.txt','w')
f.write('Mary had a little lamb,\n')
f.write('and then she had some more.\n')import os
def make_story2():
if os.path.isfile('story.txt'):
print('story.txt already exists')
else:
f=open('story.txt','w')
f.write('Mary had a little lamb,\n')
f.write('and then she had some more.\n')
>>> make_story2()
story.txt already exists附加到文字檔案末尾：
def add_to_story(line,fname='story.txt'):
f=open(fname,'a')
f.write(line)
>>> add_to_story('\nthis is append')將字串插入到檔案開頭：
def insert_title(title,fname='story.txt'):
f=open(fname,'r+')
temp=f.read()
temp=title+'\n\n'+temp
f.seek(0) # 讓檔案指標指向檔案開頭
f.write(temp)
處理二進位制檔案：
def is_gif(fname):
f=open(fname,'br')
first4=tuple(f.read(4))
return first4==(0x47,0x49,0x46,0x38)
>>> is_gif('e:/Python/timg.jpg')
False讀取網頁：（urllib模組）
>>> import urllib.request
>>> page=urllib.request.urlopen('http://www.python.org')
>>> html=page.read()
>>> html[:25]
b'<!doctype html>\n<!--[if l'（webbrowser模組）
>>> import webbrowser
>>> webbrowser.open('http://www.baidu.com')
True