常用讀寫模式：

r：讀，rb: 以二進位制形式讀
w:寫，wb: 以二進位制形式寫
a:追加
r+/w+/a+：讀寫

In [13]: df =open('/opt/1.txt','w')
write只接受字串
In [14]: df.write('aaaaaaaaaaaaaaaaaaa')
In [16]: df.close()
關閉以後才能看到內容
cat /opt/1.txt
aaaaaaaaaaaaaaaaaaaaaa

追加：
In [17]: df =open('/opt/1.txt','a')

In [18]: df.write('bbbbbbbbb')
In [19]: df.close()

cat /opt/1.txt
aaaaaaaaaaaaaaaaaaabbbbbbbbb

讀：
In [20]: df =open('/opt/1.txt')
In [21]: df.read()
Out[21]: 'aaaaaaaaaaaaaaaaaaabbbbbbbbb'
第二次讀的話就讀不到了，因為指標已到最後
 

for迴圈遍歷檔案：

讀取檔案示例：

#!/usr/bin/python
fd = open('/opt/1.txt')
for line in fd:
    print line,

[[email protected] python_test]# ./7.py
aaaaaaaaaaaaaaaaaaabbbbbbbbb
111111111111
asdas
dasd
zxc
bb

while 迴圈遍歷檔案：

用with open形式開啟一個檔案操作結束時會自動執行close()

#!/usr/bin/python

with open('/data/1.txt') as fd:
    while True:
        line = fd.readline()
        if not line:
            break
        print line,
[
 
[email protected] python_test]# ./2.py
qwe
123
ad
asd
q
1
qe

利用檔案讀寫，統計linux系統記憶體並且分析佔比

[[email protected] py]# cat mem.py
#!/usr/bin/python

def getMess(mes):
    with open ('/proc/meminfo','r') as fd:
        for f in fd:
            if f.startswith(mes):
    		m=f.split()[-2]
    return int(m)/1024.0

Totalmem=getMess('MemTotal')
MemFree=getMess('MemFree')
Buffers=getMess('Buffers')
Cached=getMess('Cached')

print ('Totalmem: %.2f' %Totalmem +'M')
print ('MemFree: %.2f' %(MemFree+Buffers+Cached) +'M','Accounted fo is %.2f%%' %((MemFree+Buffers+Cached)/Totalmem*100))
 

執行該指令碼

[[email protected] py]# python mem.py
Totalmem: 1998.15M
('MemFree: 1546.32M', 'Accounted fo is 77.39%')