from sys import argv

script,input_file=argv

def print_all(f):
    print f.read()
    
def rewind(f):
    f.seek(0)

def print_a_line(line_count,f):
    print line_count,f.readline()
    
current_file=open(input_file)

print"first let‘s print the whole file:\n"
print_all(current_file)

print"now let‘s rewind, kind of like a tape.
 
"
rewind(current_file)

print"let‘s print three lines:"
current_line=1
print_a_line(current_line,current_file)
current_line=current_line+1
print_a_line(current_line,current_file)
current_line=current_line+1
print_a_line(current_line,current_file)

常見問題之Q2: 文件中為什麽有3個空行？

函數 readline() 返回一行以 \n 結尾的文件內容， 在你調用print函數的最後增加一個逗號‘,‘，用來避免為每一行添加兩個換行符 \n

def print_a_line(line_count,f):
    print line_count,f.readline(),

笨辦法學Python：函數和文件