Python startswith and then look a word in a conditional block

Question

I have below working code which works fine, but just looking way around if there is an another elegant way of doing this, because here i'm using else condition to print the last line or dataBlock to be printed.

Note: mydudalt1 and mydudalt2 are the host names

My data File:

$ cat mydata_test.txt
-- mydudalt1 --
            192.168.2.40;       // udalt-sanjose
            192.168.2.56;       // udalt-sj1
            192.168.98.71;        // udalt-japan
            192.168.2.146;      //udalt-sj-fwd1

-- mydudalt2 --
      199.43.4.70;  // udalt-chelms
      192.168.2.56; // udalt-sj1
      192.168.98.71; // udalt-japan

My Working code:

#!/grid/common/pkgs/python/v3.6.1/bin/python3
dataBlock = ''
with open('mydata_test.txt', 'r') as frb:
    for line in frb:
        line = line.strip("\n")

        if line.startswith('--'):
            if "japan" in dataBlock:
                print(dataBlock)
            dataBlock = ''
            dataBlock = dataBlock +  line

        elif "japan" in line:
            dataBlock = dataBlock +  line
    else:
        print(dataBlock +  line)

Resulted Output:

-- mydudalt1 --            192.168.98.71;        // udalt-japan
-- mydudalt2 --      192.168.98.71; // udalt-japan

Answer 1

If "japan" only appears once in each section, you can store the startswith line, and simply print out the desired output immediately when the matching line is found:

for line in frb:
    line = line.strip("\n")

    if line.startswith("--"):
        prefix = line
    if "japan" in line:
        print(prefix + line)

Answer 2

Unless there is an indentation issue,

        dataBlock = ''
        dataBlock = dataBlock +  line

can be written:

        dataBlock = line

Answer 3

A quick Answer [Should not be used in PRODUCTION]

I mainly try to answer your concern over how to avoid "for-else" to handle last edge case, and haven't reviewed much of rest of code.

#!/grid/common/pkgs/python/v3.6.1/bin/python3

block_start_identifier = "--"
search_word = "japan"

data_block = []
block_satisfied = False

with open('mydata_test.txt', 'r') as frb:

    for line in frb.readlines():

        if line.startswith(block_start_identifier):

            # Print previous blocks
            if block_satisfied:
                print("".join(data_block))

            # Reset data blocks
            data_block = []
            block_satisfied = False

            data_block.append(line)

        elif search_word in line:
            data_block.append(line)
            block_satisfied = True

# Flush the block again as needed to handle last case
if block_satisfied:
    print("".join(data_block))
```