how can I count lines in python? code example

Example 1: python 3 text file leng

f = open("filename", "r") #Load file in any mode that's able to read, ie r, r+, w+ etc

#to get length
len(f.readlines())

#To iterate over each line
for line in f.readlines(): #file.readlines(), splits the file into a list, where each element is a seperate line
  print(line)

Example 2: Write a Python program to count the number of lines in a text file.

def countlines(fname,mode='r+'):
	count=0
	with open(fname) as f:
		for _ in f:
			count += 1
	print('total number of lines in file : ',count)

countlines('file1.txt')

##########################

with open('file1.txt') as f:
	print(sum(1 for _ in f))
##########################
with open('file1.txt') as f:
	for lno , line in enumerate(f,1):
		pass
	print('total lines:',lno)

###########################
'''You can use len(f.readlines()),
 but this will create an additional list in memory,
  which won't even work on huge files that don't fit in memory.

'''