摘要：它則是以行為單位返回字符串，也就是每次讀一行，依次循環(huán)，如果不限定，直到最后一個(gè)返回的是空字符串，意味著到文件末尾了。

在某個(gè)文件夾下面建立了一個(gè)文件，名曰：130.txt，并且在里面輸入了如下內(nèi)容：

learn python
http://qiwsir.github.io
qiwsir@gmail.com

f = open("123.txt") #打開(kāi)已經(jīng)存在的文件，此文件在當(dāng)前目錄，若在其他目錄使用絕對(duì)路徑
for line in f:
    print line, #Python 3: print(line, end="")

learn python
http://qiwsir.github.io
liuguoquan@gmail.com

緊接著做下面的操作：

>>> for line2 in f:     #在前面通過(guò)for循環(huán)讀取了文件內(nèi)容之后，再次讀取，
...     print line2         #然后打印，結(jié)果就什么也顯示，這是什么問(wèn)題？
...
>>>

這不是什么錯(cuò)誤，是因?yàn)榍耙淮我呀?jīng)讀取了文件內(nèi)容，并且到了文件的末尾了。再重復(fù)操作，就是從末尾開(kāi)始繼續(xù)讀了。當(dāng)然顯示不了什么東西，但是Python并不認(rèn)為這是錯(cuò)誤。

在這里，如果要再次讀取，那就從新f = open("130.txt")。

f = open("1234.txt","w") #創(chuàng)建文件
f.write("hello") #向文件寫(xiě)入內(nèi)容
f.close() #關(guān)閉文件流

創(chuàng)建文件，我們同樣是用open()這個(gè)函數(shù)，但是多了個(gè)"w"，這是在告訴Python用什么樣的模式打開(kāi)文件。也就是說(shuō)，用open()操作文件，可以有不同的模式?？聪卤恚?/p>

從表中不難看出，不同模式下打開(kāi)文件，可以進(jìn)行相關(guān)的讀寫(xiě)。那么，如果什么模式都不寫(xiě)，像前面那樣呢？那樣就是默認(rèn)為r模式，只讀的方式打開(kāi)文件。

使用with實(shí)現(xiàn)安全的關(guān)閉文件，不用close操作了

>>> with open("130.txt","a") as f:
...     f.write("
This is about "with...as..."")
...
>>> with open("130.txt","r") as f:
...     print f.read()
...
learn python
http://qiwsir.github.io
qiwsir@gmail.com
hello

This is about "with...as..."
>>>

import os
file_stat = os.stat("123.txt")
print file_stat

posix.stat_result(st_mode=33188, st_ino=13575445, st_dev=16777220, st_nlink=1, st_uid=501, st_gid=20, st_size=57,
st_atime=1470988267,
st_mtime=1470988267,
st_ctime=1470988267) #文件創(chuàng)建時(shí)間

read：如果指定了參數(shù)size，就按照該指定長(zhǎng)度從文件中讀取內(nèi)容，否則，就讀取全文。被讀出來(lái)的內(nèi)容，全部塞到一個(gè)字符串里面。這樣有好處，就是東西都到內(nèi)存里面了，隨時(shí)取用，比較快捷；“成也蕭何敗蕭何”，也是因?yàn)檫@點(diǎn)，如果文件內(nèi)容太多了，內(nèi)存會(huì)吃不消的。文檔中已經(jīng)提醒注意在“non-blocking”模式下的問(wèn)題，關(guān)于這個(gè)問(wèn)題，不是本節(jié)的重點(diǎn)，暫時(shí)不討論。

readline：那個(gè)可選參數(shù)size的含義同上。它則是以行為單位返回字符串，也就是每次讀一行，依次循環(huán)，如果不限定size，直到最后一個(gè)返回的是空字符串，意味著到文件末尾了(EOF)。

readlines：size同上。它返回的是以行為單位的列表，即相當(dāng)于先執(zhí)行readline()，得到每一行，然后把這一行的字符串作為列表中的元素塞到一個(gè)列表中，最后將此列表返回。

有這樣一個(gè)文檔,you.md，其內(nèi)容和基本格式如下：

    You Raise Me Up
    When I am down and, oh my soul, so weary;
    When troubles come and my heart burdened be;
    Then, I am still and wait here in the silence,
    Until you come and sit awhile with me.
    You raise me up, so I can stand on mountains;
    You raise me up, to walk on stormy seas;
    I am strong, when I am on your shoulders;
    You raise me up: To more than I can be.

分別用上述三種函數(shù)讀取這個(gè)文件。

>>> f = open("you.md")
>>> content = f.read()
>>> content #結(jié)果為字符串
"You Raise Me Up
When I am down and, oh my soul, so weary;
When troubles come and my heart burdened be;
Then, I am still and wait here in the silence,
Until you come and sit awhile with me.
You raise me up, so I can stand on mountains;
You raise me up, to walk on stormy seas;
I am strong, when I am on your shoulders;
You raise me up: To more than I can be.
"
>>> f.close()
>>> print content

>>> f = open("you.md")
>>> f.readline()
"You Raise Me Up
"
>>> f.readline()
"When I am down and, oh my soul, so weary;
"
>>> f.readline()
"When troubles come and my heart burdened be;
"
>>> f.close()

f = open("you.md")
while True:
   line = f.readline()
   if not line:         #到EOF，返回空字符串，則終止循環(huán)
       break
   print line ,         #Python 3: print(line, end="")

f.close()                #別忘記關(guān)閉文件

>>> f = open("you.md")
>>> content = f.readlines()
>>> content #結(jié)果為列表
["You Raise Me Up
", "When I am down and, oh my soul, so weary;
", "When troubles come and my heart burdened be;
", "Then, I am still and wait here in the silence,
", "Until you come and sit awhile with me.
", "You raise me up, so I can stand on mountains;
", "You raise me up, to walk on stormy seas;
", "I am strong, when I am on your shoulders;
", "You raise me up: To more than I can be.
"]

>>> for line in content:
...     print line ,         #Python 3: print(line, end="")
>>> f.close

如果文件太大，就不能用read()或者readlines()一次性將全部?jī)?nèi)容讀入內(nèi)存，可以使用while循環(huán)和readline()來(lái)完成這個(gè)任務(wù)。

此外，還有一個(gè)方法：fileinput模塊

>>> import fileinput
>>> for line in fileinput.input("you.md"):
...     print line ,        #Python 3: print(line, end="")
...
You Raise Me Up
When I am down and, oh my soul, so weary;
When troubles come and my heart burdened be;
Then, I am still and wait here in the silence,
Until you come and sit awhile with me.
You raise me up, so I can stand on mountains;
You raise me up, to walk on stormy seas;
I am strong, when I am on your shoulders;
You raise me up: To more than I can be.

還有一種方法，更為常用：

  >>> for line in f:
    ...     print line ,      #Python 3:  print(line, end="")
    ...
    You Raise Me Up
    When I am down and, oh my soul, so weary;
    When troubles come and my heart burdened be;
    Then, I am still and wait here in the silence,
    Until you come and sit awhile with me.
    You raise me up, so I can stand on mountains;
    You raise me up, to walk on stormy seas;
    I am strong, when I am on your shoulders;
    You raise me up: To more than I can be.

之所以能夠如此，是因?yàn)槲募强傻膶?duì)象，直接用for來(lái)迭代即可。

這個(gè)函數(shù)的功能是讓指針移動(dòng)。

>>> f = open("you.md")
>>> f.readline()
    "You Raise Me Up
"
    >>> f.readline()
    "When I am down and, oh my soul, so weary;
"

>>> f.seek(0)  #回到文件的最開(kāi)始位置
>>> f.readline()
    "You Raise Me Up
"

此時(shí)指針?biāo)诘奈恢?，還可以用`tell()`來(lái)顯示，如

>>> f.tell()
    17L

seek()還有別的參數(shù)，具體如下：

seek(...)
   seek(offset[, whence]) -> None.  Move to new file position.

whence的值：

默認(rèn)值是0，表示從文件開(kāi)頭開(kāi)始計(jì)算指針偏移的量（簡(jiǎn)稱偏移量）。這是offset必須是大于等于0的整數(shù)。

是1時(shí)，表示從當(dāng)前位置開(kāi)始計(jì)算偏移量。offset如果是負(fù)數(shù)，表示從當(dāng)前位置向前移動(dòng)，整數(shù)表示向后移動(dòng)。

是2時(shí)，表示相對(duì)文件末尾移動(dòng)。