Dask - concatenate two same-column dataframes doesn't work - pandas

Question

I have two dataframes without a header line, both with the same comma-separated columns.
I tried to read them into one dataframe with
dfoutputs = dd.read_csv(['outputsfile.csv', 'outputsfile2.csv'], names=colnames, header=None, dtype={'firstnr': 'Int64', 'secondnr': 'Int64', 'thirdnr': 'Int64', 'fourthnr': 'Int64'})
but this dataframe only contained outputsfile.csv rows.
Similar problem for reading and concat:
colnames=['firstnr', 'secondnr', 'thirdnr', 'fourthnr']
dfoutputs = dd.read_csv('outputsfile.csv', names=colnames, header=None, dtype={'firstnr': 'Int64', 'secondnr': 'Int64', 'thirdnr': 'Int64', 'fourthnr': 'Int64'})
print(dfoutputs.head(10))
dfoutputs2 = dd.read_csv('outputsfile2.csv', names=colnames, header=None, dtype={'firstnr': 'Int64', 'secondnr': 'Int64', 'thirdnr': 'Int64', 'fourthnr': 'Int64'})
print(dfoutputs2.head(10))
dfnew = dd.concat([dfoutputs, dfoutputs2])
print(dfnew.head(10))
Output:
firstnr secondnr thirdnr fourthnr
0 0 0 0 5000000000
1 1 0 0 5000000000
2 2 0 0 5000000000
3 3 0 0 5000000000
4 4 0 0 5000000000
5 5 0 0 5000000000
firstnr secondnr thirdnr fourthnr
0 11 0 0 5000000000
1 12 0 0 5000000000
firstnr secondnr thirdnr fourthnr
0 0 0 0 5000000000
1 1 0 0 5000000000
2 2 0 0 5000000000
3 3 0 0 5000000000
4 4 0 0 5000000000
5 5 0 0 5000000000
How can I combine both csv's to the same Dask dataframe?

Answer 1

As suggested by TennisTechBoy in the comments:
f=open("outputsfile.csv", "a")
f2=open("outputsfile2.csv", "r")
f2content = f2.readlines()
for i in range(len(f2content)):
f.write(f2content[i])
f.close()
f2.close()
A way to do this in Dask might be needed from a memory perspective.