Chris_Rands

使用无限迭代器:

from itertools import count
index = count()
self.Item = [[Object(x, y, next(index)) for y in range(3)] for x in range(3)]

令人惊讶的是,还没有人提到推荐的解决方案 in the Python 3 docs :

另见:

• 这个 linspace recipe 演示如何实现适合浮点应用程序的范围的延迟版本。

一旦定义,配方很容易使用,不需要 numpy 或任何其他外部库,但函数类似于 numpy.linspace() . 请注意,而不是 step 争论,第三个 num 参数指定所需值的数目,例如:

print(linspace(0, 10, 5))
# linspace(0, 10, 5)
print(list(linspace(0, 10, 5)))
# [0.0, 2.5, 5.0, 7.5, 10]

我引用安德鲁·巴内特(Andrew Barnert)对Python 3完整配方的修改版本如下:

import collections.abc
import numbers

class linspace(collections.abc.Sequence):
    """linspace(start, stop, num) -> linspace object

    Return a virtual sequence of num numbers from start to stop (inclusive).

    If you need a half-open range, use linspace(start, stop, num+1)[:-1].
    """
    def __init__(self, start, stop, num):
        if not isinstance(num, numbers.Integral) or num <= 1:
            raise ValueError('num must be an integer > 1')
        self.start, self.stop, self.num = start, stop, num
        self.step = (stop-start)/(num-1)
    def __len__(self):
        return self.num
    def __getitem__(self, i):
        if isinstance(i, slice):
            return [self[x] for x in range(*i.indices(len(self)))]
        if i < 0:
            i = self.num + i
        if i >= self.num:
            raise IndexError('linspace object index out of range')
        if i == self.num-1:
            return self.stop
        return self.start + i*self.step
    def __repr__(self):
        return '{}({}, {}, {})'.format(type(self).__name__,
                                       self.start, self.stop, self.num)
    def __eq__(self, other):
        if not isinstance(other, linspace):
            return False
        return ((self.start, self.stop, self.num) ==
                (other.start, other.stop, other.num))
    def __ne__(self, other):
        return not self==other
    def __hash__(self):
        return hash((type(self), self.start, self.stop, self.num))

它将更健壮,使用更简单 Biopython 为此:

from Bio import SeqIO

motif = 'GGAC'
for record in SeqIO.parse('input.fa', 'fasta'):
    if motif in record.seq:
        print(record.id)