Python 3 | Using Multiple if statements inside a for loop?

Question

I have searched and found nothing that suits my needs.

I have three for loops that each has an if conditions inside it. Here is the code:

for friend in friends:
    columns = friend.split("\n")
    if len(columns) == 4:
        c.execute("""INSERT INTO `fb_friends`(`name`, `no_of_mutual_friends`, `no_of_new_posts`, `already_friends`) VALUES (?, ?, ?, ?)""", (columns))

for friend in friends:
    columns = friend.split("\n")
    if len(columns) == 3:
        c.execute("""INSERT INTO `fb_friends`(`name`, `no_of_mutual_friends`, `already_friends`) VALUES (?, ?, ?)""", (columns))

for friend in friends:
    columns = friend.split("\n")
    if len(columns) == 2:
        c.execute("""INSERT INTO `fb_friends`(`name`, `no_of_mutual_friends`, `already_friends`) VALUES (?, ?, ?)""", (columns))

Is there a more efficient way of doing this? I was thinking of the and operator like so:

 for friend in friends:
    columns = friend.split("\n")
    if len(columns) == 4:
        c.execute("""INSERT INTO `fb_friends`(`name`, `no_of_mutual_friends`, `no_of_new_posts`, `already_friends`) VALUES (?, ?, ?, ?)""", (columns))
and
        if len(columns) == 3:
        c.execute("""INSERT INTO `fb_friends`(`name`, `no_of_mutual_friends`, `already_friends`) VALUES (?, ?, ?)""", (columns))
and
        if len(columns) == 2:
        c.execute("""INSERT INTO `fb_friends`(`name`, `already_friends`) VALUES (?, ?)""", (columns))

Can any one suggest the best or most efficient way of doing this as apposed to iterating three times over the same list?

You could avoid if statements and pad columns to size 4 instead: columns + [None]*(4-len(columns)) — jfs
– jfs, Commented Nov 12, 2016 at 16:33
I find your use of (columns) extremely misleading. It does nothing (you can replace (columns) with columns and nothing will change), but it is similar to (columns, ) (note the final comma!) which create a 1-element tuple... — Bakuriu
– Bakuriu, Commented Nov 12, 2016 at 16:52

ForceBru · Accepted Answer · 2016-11-12 16:26:56Z

3

You are looking for if/elif/else:

if len(smth) == 5:
    # do this
elif len(smth) == 6:
    # do that
else:
    # do something else

answered Nov 12, 2016 at 16:26

ForceBru

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1 Comment

Jamie Lindsey Over a year ago

Thanks ForceBru exactly what I needed.

Mehmet Hanoğlu · Accepted Answer · 2016-11-12 16:28:52Z

2

Full code here:

for friend in friends:
    columns = friend.split("\n")
    if len(columns) == 4:
        c.execute("""INSERT INTO `fb_friends`(`name`, `no_of_mutual_friends`, `no_of_new_posts`, `already_friends`) VALUES (?, ?, ?, ?)""", (columns))
    elif len(columns) == 3:
        c.execute("""INSERT INTO `fb_friends`(`name`, `no_of_mutual_friends`, `already_friends`) VALUES (?, ?, ?)""", (columns))
    elif len(columns) == 2:
        c.execute("""INSERT INTO `fb_friends`(`name`, `already_friends`) VALUES (?, ?)""", (columns))

answered Nov 12, 2016 at 16:28

Mehmet Hanoğlu

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1 Comment

Jamie Lindsey Over a year ago

Thanks MaRZoCHi exactly what I needed. I chose your answer as the correct one as it uses my original code in its example

Wera · Accepted Answer · 2016-11-12 16:39:32Z

1

reqtemplate = "INSERT INTO `fb_friends`(%s) VALUES (%s)"
fields = ['`name`', '`no_of_mutual_friends`', '`no_of_new_posts`', '`already_friends`']
for friend in friends:
    columns = friend.split("\n")
    lenc = len(columns)
    c.execute(reqtemplate % (",".join(fields[:lenc]), ",".join("?" * lenc)), (columns))

answered Nov 12, 2016 at 16:39

Wera

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4 Comments

Jamie Lindsey Over a year ago

I'm struggling to understand this code, but if I'm correct in my logic the final line here will cause the length of fields to be equal length to lenc? but I needed to cut out 'no_of_mutual_friends' & 'no_of_new_posts' not 'no_of_new_posts' & 'already_friends' when len(columns) == 2. I always have name and already_friends, but don't always have the others

Wera Over a year ago

sofields[:lenc]

Wera Over a year ago

so fields[:lenc] do this fields[:2] is from 0 included to 2 excluded: 'name', 'no_of_mutual_friends' If you always have 'name' and 'already_friends' you have to change the order in fields list

Wera Over a year ago

if already friends is always in the end, you can use other construction: fields[ : lenc-1] + fields[-1:]

John Smith · Accepted Answer · 2016-11-12 16:48:49Z

1

On top of ForceBru answer which is the cleanest one... here is an alternative one for fun.

d = {2: """INSERT INTO `fb_friends`(`name`, `no_of_mutual_friends`, `already_friends`) VALUES (?, ?, ?)""",
     3: """INSERT INTO `fb_friends`(`name`, `no_of_mutual_friends`, `already_friends`) VALUES (?, ?, ?)""",
     4: """INSERT INTO `fb_friends`(`name`, `no_of_mutual_friends`, `no_of_new_posts`, `already_friends`) VALUES (?, ?, ?, ?)"""}
for friend in friends:
    columns = friend.split("\n")
    try:
        c.execute(d[len(columns)], (columns))
    except KeyError:
        print("you sure about this columns length which was:", len(columns))

edited Nov 12, 2016 at 16:48

answered Nov 12, 2016 at 16:37

John Smith

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2 Comments

Jamie Lindsey Over a year ago

Just to point out that ForceBru and MaRZoCHi answers are basically the same with the exception that MaRZoCHi was more specific to my code, e.g. ForceBru used the numbers 5 & 6 which will never be a length of any of the columns.. and your error handler is a cool addition but is not needed if the code does not allow for any errors :/ but +1 for the use of a dict

John Smith Over a year ago

Marzochi's answer was not there when I posted :) so wasn't comparing their answers to each other but Forcebru's to mine :). And thanks, if you don't need protection of try/except you can always remove it :).

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