使用python以滑动窗口方式统计基因组fasta文件中各序列的各碱基（如GC碱基）平均含量

001、

(base) root@PC1:/home/test2# ls
a.fasta  test.py
(base) root@PC1:/home/test2# head a.fasta                  ## 测试数据
>scaffold_1
CCCGGGTAAAACGGGTCTTCAAGAAAACGCTCCTCCGTTAATGCCGGCCGATTCAAATAA
CCTCTGGCAACACCCGCTCCGGCAATGTATAGTTCACCGATACATCCAACAGGCAGCATC
CGCTGATTCTGATTCAGGATATACAATCTGACATGATGAACAGGTTTTCCAATTGGAATC
CGTTCAAGTTTTTCTTGCGGCGGACAATCAAAGAATGCAGCTTCTACGGTTGCTTCCGTT
GGCCCATAGGAATTGGTTATTGAAACATTTGGAAGCAACACGTGAAATCGGGAGACAAGA
TGGGTCCCCAGCTGTTCTCCCCCAGAAAACACTCGCTTGAGTCTGTTTGTCTTAATCGGT
ACAGAGCGATATTTTATATGTTCTAAAAATGCATGGAGCATTGAAGGCACAAAATGCATA
GCTGTGATCTTTTGTTCTTCTATGGCCTTCGCGATCACTTCAGGTTCTTTTTCGCCTCCC
TGAGGAAGCAGATAAACAGAAGCTCCGGCATAAGGCCACCAAAACAGCTCCCATATTGAA
(base) root@PC1:/home/test2# cat test.py                   ## 测试程序
#!/usr/bin/python

import re
in_file = open("a.fasta", "r")
out_file = open("result.txt", "w")
dict1 = dict()

for i in in_file:
    i = i.strip()
    if i[0] == ">":
        key = i
        dict1[key] = ""
    else:
        dict1[key] += i

step = 5000
print("id", "start", "end", "a", "c", "g", "t", "cg", file = out_file, sep = "\t")

for i,j in dict1.items():
    length = len(j)
    start = 0
    if length < step and start == 0:
        block = j[::]
        a = len(re.findall("[aA]", block))
        c = len(re.findall("[cC]", block))
        g = len(re.findall("[gG]", block))
        t = len(re.findall("[tT]", block))
        cg = len(re.findall("[cCgG]", block))
        len_block = len(block)
        print(i, 1, len(j), a/len_block, c/len_block, g/len_block, t/len_block, cg/len_block, file = out_file, sep = "\t")

    while length > step:
        end = start + step
        block = j[start:end]
        a = len(re.findall("[aA]", block))
        c = len(re.findall("[cC]", block))
        g = len(re.findall("[gG]", block))
        t = len(re.findall("[tT]", block))
        cg = len(re.findall("[cCgG]", block))
        len_block = len(block)
        print(i, start + 1, end, a/len_block, c/len_block, g/len_block, t/len_block, cg/len_block, file = out_file, sep = "\t")

        start += step
        length -= step

        if length < step:
            block = j[end::]
            a = len(re.findall("[aA]", block))
            c = len(re.findall("[cC]", block))
            g = len(re.findall("[gG]", block))
            t = len(re.findall("[tT]", block))
            cg = len(re.findall("[cCgG]", block))
            len_block = len(block)
            print(i, end, len(j), a/len_block, c/len_block, g/len_block, t/len_block, cg/len_block, file = out_file, sep = "\t")

in_file.close()
out_file.close()

(base) root@PC1:/home/test2# python test.py                          ## 运行程序
(base) root@PC1:/home/test2# ls
a.fasta  result.txt  test.py
(base) root@PC1:/home/test2# head result.txt                         ## 运行结果
id      start   end     a       c       g       t       cg
>scaffold_1     1       5000    0.2562  0.2254  0.2242  0.2942  0.4496
>scaffold_1     5001    10000   0.2416  0.233   0.2286  0.2968  0.4616
>scaffold_1     10001   15000   0.249   0.2544  0.221   0.2756  0.4754
>scaffold_1     15001   20000   0.2556  0.2422  0.2158  0.2864  0.458
>scaffold_1     20001   25000   0.2604  0.2352  0.2104  0.294   0.4456
>scaffold_1     25001   30000   0.2524  0.2404  0.219   0.2882  0.4594
>scaffold_1     30001   35000   0.3002  0.219   0.1934  0.2874  0.4124
>scaffold_1     35001   40000   0.287   0.219   0.2126  0.2814  0.4316
>scaffold_1     40001   45000   0.2424  0.25    0.2096  0.298   0.4596

参考：https://mp.weixin.qq.com/s?__biz=MzIxNzc1Mzk3NQ==&mid=2247491497&idx=1&sn=5759613bc25c175b71aaf5a5091d0a51&chksm=97f5afb1a08226a7b9eac750c7df99fdd6b5ec110f2f21e79ee0ef542caf93c8105d9b5358c4&scene=178&cur_album_id=2403674812188688386#rd