I find a funny things in readline() method:

Question

a file name '123' which contain:'1. first line
2. second line
3. third line'
so right now when I input these code:
```python
a = open('123','r')
while a.readline() != '':
    print(a.readline())
the result will always only print 2.second line

so I suspect if because when I use a.readline(), I don't give him a variable name, so I change the code into this:
a = open('123','r')
b = a.readline()
while b != '':
    print(b)
when I test the obove code ,there is loop infinit, so I guess that is because b is the first line which is '1.first line', so even ## the loop, so it still b.
But when I do this code:
a = open('123','r')
b = a.readline()
c = a.readline()
d = a.readline()
e = a.readline() 
b = '1. first line
' , c = '2. second line
' , d = '3. third line', e = ''
```
so I don't know why does those things happened. 
I don't know why , thank you for help me.
[MOD: edited code block]

Chris Freeman · Accepted Answer

In your code, the first example consumes a line during the while test, so the print will see line 2 first.  The second example  b is assigned outside of the loop so its value does not change causing an infinite loop.
From the python docs 'iter' (https://docs.python.org/2/library/functions.html#iter) has a solution
python
for line in iter(a.readline, ''):
    print(line)

Or use in:
python
a = open("123", 'r')
for line in a:
    print(line)

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I find a funny things in readline() method:

1 Answer

Chris Freeman

Chris Freeman

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