python - urllib.request.urlretrieve throws unexpected exception unknown url type: ' ' - urllib

Question

I am trying to download files using urllib.request.retrieve()
I am using Python 3 and the downloads are successful, but I don't know why it throws exception.
For some reason it throws an exception.
This is the main file:
import os
import urllib.request
zip_file_open = open("urls.txt")
if not os.path.exists('zip'):
os.makedirs('zip')
num=1
true = True
b = true
for i in zip_file_open.read().splitlines():
try:
print(str(i))
#response = urllib.request.urlopen(str(i))
#print(response)
#html = response.read()
urllib.request.urlretrieve(i, "zip/code"+str(num)+".zip")
if(b):
num+=1
b=False
else:
b=true
except Exception as e:
print("Exception: "+str(e))
if(b):
num+=1
b=False
else:
b=true
This is urls.txt:
http://media.wiley.com/product_ancillary/50/11188580/DOWNLOAD/c01_code.zip
http://media.wiley.com/product_ancillary/50/11188580/DOWNLOAD/c02_code.zip
........
http://media.wiley.com/product_ancillary/50/11188580/DOWNLOAD/c25_code.zip
http://media.wiley.com/product_ancillary/50/11188580/DOWNLOAD/c26_code.zip
Here is how I create the txt file:
f = open("urls.txt","w")
k = """http://media.wiley.com/product_ancillary/50/11188580/DOWNLOAD/c"""
k1 = """_code.zip"""
import os
for i in range(26):
if(i<9):
f.write(k+str(0)+str(i+1)+k1+os.linesep)
else:
f.write(k+str(i+1)+k1+os.linesep)
f.close()
Here is the output
http://media.wiley.com/product_ancillary/50/11188580/DOWNLOAD/c01_code.zip
Exception2: unknown url type: ''
http://media.wiley.com/product_ancillary/50/11188580/DOWNLOAD/c02_code.zip
Exception3: unknown url type: ''
http://media.wiley.com/product_ancillary/50/11188580/DOWNLOAD/c03_code.zip
Exception3: HTTP Error 404: Not Found
........
Exception26: unknown url type: ''
http://media.wiley.com/product_ancillary/50/11188580/DOWNLOAD/c26_code.zip
Exception27: unknown url type: ''
I didn't include all the lines of output as they were same. The code is functional but I would like to know if we can remove the exception.

Answer 1

It looks like you have some blank lines in your file, so urllib throws a ValueError exception when you try to fetch '', which is clearly not a url.
You can fix this error if you add a condition in the loop to check for empty strings.
for i in zip_file_open.read().splitlines():
if not i.strip():
continue
...
But this won't work for non-empty strings that are not urls, for example 'not a url'.
A better approach would be to check the url scheme with urlparse.
for i in zip_file_open.read().splitlines():
if not urllib.parse.urlparse(i).scheme:
continue
...