######################################################
### Open the file reads.fastq for reading as text
###
### Initialise a Count for the Reads with low  Accession Codes.
### Initialise a Count for the Reads with high Accession Codes.
###
### Keep reading the file one line at a time until reaching an
### Accession Code with a high value.
###
###    if the Current Line begins with an "@SRR"
###        if the Accession Code is low enough
###           print it out
###           Add 1 to the Count of low Accession Code Reads
###        otherwise break off this inteation through the file.
###
### Continue reading through the file until the bitter end
### 
###     if the Current Line begins with an "@SRR"
###         Add 1 to the Count of high Accession Code Reads
###
### Announce the requested Read Counts
###
### Close the file.
###
#######################################################

Fastq_File = open("reads.fastq")  # Open input file, requesting
                                  # read & text (the defaults)
                                  # implicitly

Read_Count_hi = Read_Count_lo = 0 # Initialise low and high Read Counts

for Line in Fastq_File:       # For each Line of the fastq file, in turn,
    if Line[0:4] == '@SRR':   # if it is the first line of a new read,
        Acc_int = int(Line[12:].rstrip())
        if Acc_int < 124000:
                              # and if the Accession Code is low enough,
            print(Line, end = '')
                              # print it out,
            Read_Count_lo += 1
                              # and add 1 to the count of low Accession reads.
        else:                 # Otherwise,
            break             # Stop reading lines from the file.

while Line:                   # Until the End of the File
    if Line[0:4] == '@SRR':     # if the current line is the first line of a read,
        Read_Count_hi += 1    # increment the count of high Accession reads.

    Line = Fastq_File.readline()
                              # Read the next line of the file and go round again.

# Declare the Counts of Reads.
print("The low   Accession Read count for reads.fastq is " \
                        + str(Read_Count_lo))
print("The high  Accession Read count for reads.fastq is " \
                        + str(Read_Count_hi))
print("The total Accession Read count for reads.fastq is " \
                        + str(Read_Count_lo + Read_Count_hi))