Python 中File I/O 和一些常用的方法

>>> strings = """\I'm a great man who was born in China
I was born to give and give and give
This is a new line
And this is another new line"""
>>> file.write(strings)
123                  #此處表示寫入的內容總共有多少byte
>>> file.close()

>>> file = open("output.txt","rt")
>>> print(file.read())
\I'm a great man who was born in China
I was born to give and give and give
This is a new line
And this is another new line
>>> print(file.read())
#這裏將會是空白，因為此刻指針（光標）的位置處於段落末尾

1. seek()

seek可以用來改變當前object的位置（例如file read之後），通常的格式seek(offset, from_what)。

The position is computed from adding offset to a reference point; the reference point is selected by the from_what argument. A from_what value of 0 measures from the beginning of the file, 1 uses the current file position, and 2 uses the end of the file as the reference point. from_what can be omitted and defaults to 0, using the beginning of the file as the reference point.

默認隻有一個參數，就表示從文件開始的位置(0)，因此，seek(0)就表示目前是處於文件的開頭，第二個參數表示從哪裏開始計算，0表示開頭，也是默認的，1表示當前位置，2表示末尾。

>>> file.seek(0)
0#當前位置
>>> print(file.read())
\I'm a great man who was born in China
I was born to give and give and give
This is a new line
And this is another new line

2. 利用list，將file中的文字存入到list中
file有一個函數readlines()，注意此函數和readline()有區別，readline是一次讀取一行，而readlines()是將所有數據存入list中，每一行作為list的一個element，如此之後，即便我們close的文件，依舊可以繼續打印文件裏已經存儲在list中的內容了。

>>> x = file.readlines()#錯誤，注意此時的位置已經處於末尾了
>>> print(x)
[]#所以打印出來的內容為空
>>> print(x[0])
Traceback (most recent call last):
  File "<pyshell#7>", line 1, in <module>
    print(x[0])
IndexError: list index out of range
>>> file.seek(0)#將位置置於開頭
0
>>> x = file.readlines()
>>> print(x)
["\\I'm a great man who was born in China\n", 'I was born to give and give and give\n', 'This is a new line\n', 'And this is another new line']
>>> print(x[0])#打印list的各項內容
\I'm a great man who was born in China
	
>>> file.close()#即便關閉了file，也可以繼續操作，因為內容已經存儲到了list中

>>> print(x[0])
\I'm a great man who was born in China

>>> print(x[3])
And this is another new line
>>> 

代碼中我犯了一個錯誤，第一次沒有將位置seek到開頭，所以第一次沒有將lines存入到x中，也就是說，若想把每一行存入到list中，也需要將當前位置置於0