Return regular expression only one time - python-3.x

Question

I am trying to have regular expression only print the result one time. Is there any suggestions? Since I want the code to read the entire text file, but there are many dates that are the same, but I just want the code to return that date one time only.
code:
import re
filename = set(open('wireshark.txt', 'r'))
pattern_object = re.compile(r'(\d\d\d\d-\d\d-\d\d)')
for line in filename:
match_object = pattern_object.search(line)
if match_object:
regex = match_object.group(1)
print(regex)
Text file:
No. Time Source Destination Protocol Length Info
2 2021-02-12 13:33:12.206424 192.168.1.151 172.217.10.46 QUIC 1392 Initial, DCID=e4267bae554f387d, PKN: 1, CRYPTO, PADDING
Frame 2: 1392 bytes on wire (11136 bits), 1392 bytes captured (11136 bits) on interface \Device\NPF_{28AA034F-AC94-4D4A-9CA9-9AEA5D0EF2C1}, id 0
Ethernet II, Src: Micro-St_0e:cd:34 (00:d8:61:0e:cd:34), Dst: Verizon_fb:8b:82 (20:c0:47:fb:8b:82)
Internet Protocol Version 4, Src: 192.168.1.151, Dst: 172.217.10.46
User Datagram Protocol, Src Port: 57189, Dst Port: 443
QUIC IETF
No. Time Source Destination Protocol Length Info
3 2021-02-12 13:33:12.225610 172.217.10.46 192.168.1.151 QUIC 1392 Initial, SCID=e4267bae554f387d, PKN: 1, ACK, CRYPTO, PADDING
Frame 3: 1392 bytes on wire (11136 bits), 1392 bytes captured (11136 bits) on interface \Device\NPF_{28AA034F-AC94-4D4A-9CA9-9AEA5D0EF2C1}, id 0
Ethernet II, Src: Verizon_fb:8b:82 (20:c0:47:fb:8b:82), Dst: Micro-St_0e:cd:34 (00:d8:61:0e:cd:34)
Internet Protocol Version 4, Src: 172.217.10.46, Dst: 192.168.1.151
User Datagram Protocol, Src Port: 443, Dst Port: 57189
QUIC IETF
No. Time Source Destination Protocol Length Info
4 2021-02-12 13:33:12.225989 192.168.1.151 172.217.10.46 TLSv1.2 146 Application Data
No. Time Source Destination Protocol Length Info
4 2021-04-12 13:33:12.225989 192.168.1.151 172.217.10.46 TLSv1.2 146 Application Data
No. Time Source Destination Protocol Length Info
4 2021-06-12 13:33:12.225989 192.168.1.151 172.217.10.46 TLSv1.2 146 Application Data
No. Time Source Destination Protocol Length Info
4 2021-06-12 13:33:12.225989 192.168.1.151 172.217.10.46 TLSv1.2 146 Application Data
Code execute output:
2021-02-12
2021-02-12
2021-02-12
2021-02-12
2021-02-12
2021-02-12
2021-04-12
2021-06-12
2021-06-12
desire code execute output:
2021-02-12
2021-04-12
2021-06-12

Answer 1

Here's a minimal example for how to get all the unique dates in the file.
Essentially, it's a 4 stage process:
Store the pattern to search for as a string
Open the file and get all the text
Use re.findall() to get all of the text matching the pattern
Use set() to keep only the unique matches
import re
# Make the pattern
pattern = '(\d\d\d\d-\d\d-\d\d)'
# Open the file and read all the text into a variable
with open('wireshark.txt') as file:
text = file.read()
# Search the text for anything matching the pattern
matches = re.findall(pattern, text)
# Print the unique matches
print(set(matches))
The key thing here is the combination of re.findall() (search for multiple matches at once) and set() (to get rid of duplicates.