Python基础：iter函数的两个参数

<p style="line-height: 1.75em;"><span style="font-family: 微软雅黑, "Microsoft YaHei";">l = [1, 2, 3]

  for i in iter(l):

      print(i)<br></span></p>

<p style="line-height: 1.75em;"><span style="font-family: 微软雅黑, "Microsoft YaHei";">    class TestIter(object):

        def __init__(self):

            self.l=[1,2,3,4,5]

            self.i=iter(self.l)

        def __call__(self):  #定义了__call__方法的类的实例是可调用的

            item = next(self.i)

            print ("__call__ is called,which would return",item)

            return item

        def __iter__(self): #支持迭代协议(即定义有__iter__()函数)

            print ("__iter__ is called!!")

            return iter(self.l)

    t = TestIter()  # t是可调用的

    t1 = iter(t, 3)  # t必须是callable的，否则无法返回callable_iterator

    print(callable(t))

    for i in t1:

        print(i)

# 它每次在调用的时候，都会调用__call__函数，并且最后输出3就停止了。

True

__call__ is called,which would return 1

1

__call__ is called,which would return 2

2

__call__ is called,which would return 3<br></span></p>

<p style="line-height: 1.75em;"><span style="font-family: 微软雅黑, "Microsoft YaHei";">import os

import hashlib

def bytes2human(n):

    # 文件大小字节单位转换

    symbols = ('K', 'M', 'G', 'T', 'P', 'E')

    prefix = {}

    for i, s in enumerate(symbols):

        # << 左移” 左移一位表示乘2 即1 << 1=2，二位就表示4 即1 << 2=4，

        # 10位就表示1024 即1 << 10=1024 就是2的n次方

        prefix[s] = 1 << (i + 1) * 10

    for s in reversed(symbols):

        if n >= prefix[s]:

            value = float(n) / prefix[s]

            return '%.2f%s' % (value, s)

    return "%sB" % n

def get_md5(file_path):

    """

    得到文件MD5

    :param file_path:

    :return:

    """

    if os.path.isfile(file_path):

        file_size = os.stat(file_path).st_size

        md5_obj = hashlib.md5()  # hashlib

        f = open(file_path, 'rb')  # 打开文件

        read_size = 0

        while read_size < file_size:

            read_byte = f.read(8192)

            md5_obj.update(read_byte)  # update md5

            read_size += len(read_byte)

        hash_code = md5_obj.hexdigest()  # get md5 hexdigest

        f.close()

        print('file: [{}] \nsize: [{}] \nmd5: [{}]'.format(

            file_path, bytes2human(read_size), hash_code))

        return str(hash_code)

def get_filemd5(file_path):

    # 使用迭代器读取文件获得MD5

    if os.path.isfile(file_path):

        file_size = os.stat(file_path).st_size

        md5_obj = hashlib.md5()  # hashlib

        f = open(file_path, 'rb')  # 打开文件

        read_size = 1024

        for chunk in iter(lambda: f.read(read_size), b''):  # 使用迭代器读取文件获得MD5

            md5_obj.update(chunk)

        hash_code = md5_obj.hexdigest()  # get md5 hexdigest

        f.close()

        print('file: [{}] \nsize: [{}] \nmd5: [{}]'.format(

            file_path, bytes2human(file_size), hash_code))

        return str(hash_code)

if __name__ == '__main__':

    md5 = get_md5(

        r'C:\README.md')

    md5_1 = get_filemd5(

        r'C:\README.md')

------------------------输出

file: [C:\README.md]

size: [941B]

md5: [d22b8f76dcd8cfbfd4669d9d8101077e]

file: [C:\README.md]

size: [941B]

md5: [d22b8f76dcd8cfbfd4669d9d8101077e]<br></span></p>