python 教程：read()，readline() 和 readlines() 比较

共同点：均可接受一个变量用以限制每次读取的数据量，但通常不使用

区别：

read() 【即 fileObject().read( [size] ) 】

特点：读取整个文件，将文件内容放在一个字符串变量中。

劣势：如果文件非常大，尤其大于内存时，无法使用read()方法。

with open(r'../learn_file/file_to_read.txt', encoding='utf-8', mode='r') as fb:
    content = fb.read()
    print(type(content))
    print(content)
# 输出：
# <class 'str'>
# line 1: Hello, Mike.
# line 2: Nice to meet you. I'm Nick.
# line 3: Welcome to Shenzhen.
# line 4: Thx, it is really a beautiful city. I enjoy my time here.
# line 5: It is. Shall we go for some coffee this afternoon.
# line 6：Sure. And I want to discuss some details about the project we're going to work for

readline() 【即 fileObject.readline( [size] )，[size]表示可选参数。】

特点：从文件中一行一行地整行读取数据，如果指定了一个非负数的参数，则返回指定大小的字节数。

缺点：比readlines()慢得多

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with open(r'../learn_file/file_to_read.txt', encoding='UTF-8', mode='r+') as fb:
    while True:
        content = fb.readline().replace('\n', '')
        # content = fb.readlines()
        # if not content:
        #     break
        if content:
            print(type(content), content)
        else:
            break
        # print(type(content))
        # print(type(content), content)
    print(fb.name)
# 输出：
# <class 'str'> line 1: Hello, Mike.
# <class 'str'> line 2: Nice to meet you. I'm Nick.
# <class 'str'> line 3: Welcome to Shenzhen.
# <class 'str'> line 4: Thx, it is really a beautiful city. I enjoy my time here.
# <class 'str'> line 5: It is. Shall we go for some coffee this afternoon.
# <class 'str'> line 6：Sure. And I want to discuss some details about the project we're going to work for.
# ../learn_file/file_to_read.txt

readlines() 【即 fileObject.readlines( [sizeint] )，[sizeint] 表示可选参数】

特点：从文件一次读取所有行并返回列表，若给定sizeint > 0，返回总和大约为sizeint字节的行

with open(r'../learn_file/file_to_read.txt', encoding='utf-8', mode='r') as fb:
    content = fb.readlines()
    print(type(content))
    for line in content:
        print(type(line), line.replace('\n', ''))
# 输出
# <class 'list'>
# <class 'str'> line 1: Hello, Mike.
# <class 'str'> line 2: Nice to meet you. I'm Nick.
# <class 'str'> line 3: Welcome to Shenzhen.
# <class 'str'> line 4: Thx, it is really a beautiful city. I enjoy my time here.
# <class 'str'> line 5: It is. Shall we go for some coffee this afternoon.
# <class 'str'> line 6：Sure. And I want to discuss some details about the project we're going to work for.