目錄

基本步驟

常用函數(shù)

open()函數(shù)

close()函數(shù)

read()函數(shù)

readlines()函數(shù)

readline()函數(shù)

write()函數(shù)

writelines()函數(shù)

with語(yǔ)句

讀寫(xiě)操作的應(yīng)用：

拷貝文件

?with 語(yǔ)句的嵌套

逐行拷貝

基本步驟

1. 打開(kāi)文件：open(filepath, mode, encoding)

2. 讀寫(xiě)文件：read() / write()

3. 關(guān)閉文件：close()

python讀取文件操作實(shí)例
f = open('filename.txt', 'r', encoding='utf-8')
f.read()
f.close()

常用函數(shù)

open()函數(shù)

open(file, mode='r', buffering=-1, encoding=None, errors=None, newline=None, closefd=True, opener=None)

file是要打開(kāi)的文件，mode='r'是打開(kāi)文件的模式，encoding是編碼格式

文件的打開(kāi)模式有以下字符表示：

? ? 'r' ? ? ? open for reading (default)
? ? 'w' ? ? ? open for writing, truncating the file first
? ? 'x' ? ? ? create a new file and open it for writing
? ? 'a' ? ? ? open for writing, appending to the end of the file if it exists
? ? 'b' ? ? ? binary mode
? ? 't' ? ? ? text mode (default)
? ? '+' ? ? ? open a disk file for updating (reading and writing)

打開(kāi)模式還能連用：

The default mode is 'rt' (open for reading text). For binary random? access, the mode 'w+b' opens and truncates the file to 0 bytes, while?'r+b' opens the file without truncation. The 'x' mode implies 'w' and?raises an `FileExistsError` if the file already exists.

close()函數(shù)

close() method of _io.TextIOWrapper instance
? ? Flush and close the IO object.

? ? This method has no effect if the file is already closed

打開(kāi)文件，必須有對(duì)應(yīng)的關(guān)閉，否則該未關(guān)閉的文件不能被其它的應(yīng)用操作。

read()函數(shù)

read(size=-1, /) method of _io.TextIOWrapper instance
? ? Read at most size characters from stream.

? ? Read from underlying buffer until we have size characters or we hit EOF.
? ? If size is negative or omitted, read until EOF.

read()可選參數(shù)size可以用于讀取“size”大小的數(shù)據(jù)，返回的是字符串或字節(jié)對(duì)象，若是size的值沒(méi)有填寫(xiě)，或者是個(gè)負(fù)值，那么read()函數(shù)將讀取文件的所有內(nèi)容，這也是用python開(kāi)發(fā)pc軟件中“復(fù)制黏貼”的功能比較常用的函數(shù)。

readlines()函數(shù)

Help on built-in function readlines:

readlines(hint=-1, /) method of _io.TextIOWrapper instance
? ? Return a list of lines from the stream.

? ? hint can be specified to control the number of lines read: no more
? ? lines will be read if the total size (in bytes/characters) of all
? ? lines so far exceeds hint.

readlines()函數(shù)是將文件當(dāng)中的所有行，一行一行地讀取，并逐一寫(xiě)入一個(gè)列表list內(nèi)，最終返回這個(gè)列表。

readline()函數(shù)

Help on built-in function readline:

readline(size=-1, /) method of _io.TextIOWrapper instance
? ? Read until newline or EOF.

? ? Return an empty string if EOF is hit immediately.
? ? If size is specified, at most size characters will be read.

readline()函數(shù)就是讀取一行數(shù)據(jù)，用法除了size參數(shù)之外，就跟read()差不多，也是open()打開(kāi)文件，readline()讀取數(shù)據(jù)，close()關(guān)閉文件

write()函數(shù)

write(text, /) method of _io.TextIOWrapper instance
? ? Write string s to stream.

? ? Return the number of characters written
? ? (which is always equal to the length of the string).

writelines()函數(shù)

writelines(lines, /) method of _io.TextIOWrapper instance
? ? Write a list of lines to stream.

? ? Line separators are not added, so it is usual for each of the
? ? lines provided to have a line separator at the end.

with語(yǔ)句

通過(guò)with語(yǔ)句，不管讀取還是寫(xiě)入文件操作都不用寫(xiě)對(duì)應(yīng)的close()函數(shù)，語(yǔ)句塊結(jié)束系統(tǒng)會(huì)自動(dòng)關(guān)閉文件。

with open('filename.txt', 'r', encoding='urf-8') as f:
? ? f.read()

讀寫(xiě)操作的應(yīng)用：

拷貝文件

# 打開(kāi)源文件以讀取內(nèi)容  
with open('source.txt', 'r') as source_file:  
    source_content = source_file.read()  
  
# 打開(kāi)目標(biāo)文件以寫(xiě)入內(nèi)容  
with open('destination.txt', 'w') as destination_file:  
    destination_file.write(source_content)

?with 語(yǔ)句的嵌套

以上兩個(gè)with語(yǔ)句塊還能嵌套寫(xiě)在一起：

# 打開(kāi)源文件以讀取內(nèi)容，并同時(shí)打開(kāi)目標(biāo)文件以寫(xiě)入內(nèi)容  
with open('source.txt', 'r') as source_file:  
    with open('destination.txt', 'w') as destination_file:  
        # 讀取源文件的內(nèi)容  
        source_content = source_file.read()  
        # 將讀取的內(nèi)容寫(xiě)入到目標(biāo)文件中  
        destination_file.write(source_content)

可以寫(xiě)在同一行：

# 打開(kāi)源文件以讀取內(nèi)容，并同時(shí)打開(kāi)目標(biāo)文件以寫(xiě)入內(nèi)容  
with open('source.txt', 'r') as source_file, open('destination.txt', 'w') as destination_file:  
    # 讀取源文件的內(nèi)容  
    source_content = source_file.read()  
    # 將讀取的內(nèi)容寫(xiě)入到目標(biāo)文件中  
    destination_file.write(source_content)

逐行拷貝

如果源文件很大，使用read()方法一次性讀取所有內(nèi)容可能會(huì)消耗較多的內(nèi)存。對(duì)于大文件，更推薦的做法是使用文件對(duì)象的迭代器逐行讀取和寫(xiě)入，這樣可以減少內(nèi)存的使用。

with open('source.txt', 'r') as source_file, open('destination.txt', 'w') as destination_file:  
    # 逐行讀取源文件并寫(xiě)入目標(biāo)文件  
    for line in source_file:  
        destination_file.write(line)

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