python readline沒有給出預期的輸出

Question

from sys import argv 

script,inputfile=argv 

def print_all(file): 
    print(file.read()) 

def rewind(file): 
    file.seek(0) 

def print_line(line,file): 
    print(line,file.readline()) 

currentFile=open(inputfile) 

print("Let's print the first line: \n") 

print_all(currentFile) 

print("Rewind") 
rewind(currentFile) 

currentLine=1 

print_line(currentLine,currentFile) 

currentLine+=1 

print_line(currentLine,currentFile) 


currentLine+=1 


print_line(currentLine,currentFile) 

我有這段代碼，這個工程，但我不明白的是，當我重寫打印語句在打印行函數打印（file.readline（line））我得到意想不到的輸出。我使用Python 3.6

正確的輸出

This is line 1 
This is line 2 
This is line 3 
Rewind 
This is line 1 

This is line 2 

This is line 3 

不正確的輸出

This is line 1 
This is line 2 
This is line 3 
Rewind 
T 
hi 
s i 

爲什麼會發生這種情況？

Answer 1

這是因爲file.readline()函數定義的，

readline(...) 
    readline([size]) -> next line from the file, as a string. 

    Retain newline. A non-negative size argument limits the maximum 
    number of bytes to return (an incomplete line may be returned then). 
    Return an empty string at EOF. 

因此，當傳遞線數作爲參數，你是actullay告訴它獲取與每個currentLine+=1遞增字節數。

如果你只是打算打印由線內容行，你可以參考這個，

def print_file_line_by_line(currentFile): 
    for line in currentFile: 
     print line.strip('\n') 

或者這也適用

def print_file_line(currentLine, currentFile): 
    try: 
     print currentFile.read().split('\n')[currentLine-1] 
    except IndexError as e: 
     print str(currentLine)+' is greater than number of lines in file' 
     print ''+str(e)