python 文件插入第一行

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def file_insert(fname,linenos=[],strings=[]):  
"""
Insert several strings to lines with linenos repectively.
The elements in linenos must be in increasing order and len(strings)
must be equal to or less than len(linenos).
The extra lines ( if len(linenos)> len(strings)) will be inserted
with blank line.
"""  
if os.path.exists(fname):  
lineno = 0  
i = 0  
for line in fileinput.input(fname,inplace=1):  
# inplace must be set to 1  
# it will redirect stdout to the input file  
lineno += 1  
line = line.strip()  
if i<len(linenos) and linenos==lineno:  
if i>=len(strings):  
print "\n",line  
else:  
print strings  
print line  
i += 1  
else:  
print line
　　fileinput.input的inplace必须要设为1，以便让stdout被重定向到输入文件里：
　　file_insert('a.txt'
,[
1
,
4
,
5
],[
'insert1'
,
'insert4'
]