The following code searches a specific substring  in all 'txt' file in a directory.

```
import os
import time
directory = 'D:/Python/file1/'

for filename in os.listdir(directory):
	filesize = os.stat(filename).st_size
	if (filesize>60000):
		continue
	# print(filename)
	
	with open(filename, 'rb') as f:
		lines = f.readlines()
		for line in lines:
			tempstr = str(line)
			le = len(tempstr)
			#print(tempstr)
			findresults=tempstr.find("binance")	
			#print(findresults)
			# time.sleep(5)
			if (findresults!=-1):
				print(filename)
				print(tempstr)
```