Python Files, Reading

Our "source.txt" is simple, just three lines.

Use "f" as handle for operation. We will just read() all lines, so "r" is second argument:

f = open("source.txt", "r")

result = f.read()

print(result)

Result: 

first line
second line
third line

>>> 

If you need to read just specific number of bytes, you can pass that as argument:

f = open("source.txt", "r")

print(f.read(5))
print(f.read(5))
print(f.read(5))

Result:  

first
 line

seco
>>> 

For loops are also great here:

f = open("source.txt", "r")

for x in range(3):
    print(f.read(6))

Result:  

first 
line
s
econd 
>>> 

With function readline() we can read line by line:

f = open("source.txt", "r")

print(f.readline())
print(f.readline())
print(f.readline())

Result:  

first line

second line

third line

>>> 

If you need to extract all lines to list, use readlines() function:

f = open("source.txt", "r")

all_lines = f.readlines()

print(all_lines)
print(type(all_lines))

Result:  

['first line\n', 'second line\n', 'third line\n']
<class 'list'>
>>> 

Then we can target individual lines as elements:

f = open("source.txt", "r")

all_lines = f.readlines()

print(all_lines[0])
print(all_lines[1])
print(all_lines[2])

Result:  

first line

second line

third line

>>> 

Easy.

It't time to learn how to write and append to files.