How to reverse words in string using python using for loop?

Question

How to reverse words in string in python using for loop? EX- "HELLO WORLD" to "WORLD HELLO"

str="HELLO WORLD"

Answer 1

I'm coming up with a comprehensive answer:

Here's what you want, just bare* python constructs:

input = 'Hello'
word = ' '
output = ''
for c in input:
    if c == ' ':
        output = word + output
        word = ' '
    else:
        word += c
output = word[1:] + output

It's just iterating over all letters and keeps them until a word is built. When current character c is a space, it prepends current word to the output string. After the for-loop there's a need to prepend the last word to output. It has to be done manually since there's no whitespace at the end of a string you provided. word[1:] just removes and extra space from the last word.

But the above solution isn't really effective since many string creations and concatenations are used. If you want to create a compact and pythonic solution, here's one:

input = "Hello world"
output = ' '.join(reversed(input.split()))

1. input.split() turns input into a list ['Hello', 'world']

2. reversed(...) turns the list into ['world', 'Hello']

3. ' '.join(...) concatenates each string in the list ['world', 'Hello'] with a space between each pair of words, so the result is 'world Hello'.

Quick and dirty, isn't it?

_{*bare - what OP claimed as without using any internal function}

Answer 2

' '.join(str.split(" ")[-1::-1]) 

output:

WORLD HELLO

With for-loop

outputLst =[]

words = str.split(" ")
for word in words:   
    outputLst.insert(0, word)
' '.join(outputLst)

output:

`WORLD HELLO`

Answer 3

You don't need a for-loop for that: just use the position of the space-character, as you can see in following pseudo-code:

int i_space = location(" ", "HELLO WORLD"")
result = substring("HELLO WORLD", 1, i_space - 1) + " " + substring("HELLO WORLD", i_space + 1, Length("HELLO WORLD"))

A for-loop is more useful for handling more elaborate cases, like:

HELLO THIS IS A BEAUTIFUL WORLD => transfer into:
WORLD BEAUTIFUL A IS THIS HELLO

Or:

HELLO WORLD => transfer into:
DLROW OLLEH

Does this answer your question?

Answer 4

str="HELLO WORLD"
rev=""
for i in range(len(str.split(" "))):
    rev=str.split(" ")[i]+" "+rev

Output: WORLD HELLO

Another solution for not using the builtin function:

def split(str):
    list_str=[]
    j=0;
    for i in range(len(str)):
        if str[i]==' ':
            list_str.append(str[j:i])
            j=i+1;
    list_str.append(str[j:i+1])
    return list_str


str="HELLO WORLD"
rev=""
list_str=split(str)
for i in range(len(list_str)):
    rev=list_str[i]+" "+rev
print(rev)

Output: WORLD HELLO

Answer 5

a gentle progression of solutions:

first, the naive one:

text = 'hello world'

words = text.split()  # words = ['hello', 'world']
line = []
for i in range(len(words), 0, -1):  # iterate i over [2, 1]
    line.append(words[i - 1])  # append 'hello' then 'world' to line
print(' '.join(line))  # join the contents of line together with spaces and print

next we use the reversed iterator:

words = text.split()
line = []
for i in reversed(range(len(words))):
    line.append(words[i])
print(' '.join(line))

next we use the list iterator:

words = text.split()
line = []
for word in reversed(words):
    line.append(word)
print(' '.join(line))

finally, we do everything with an implicit loop:

print(' '.join(reversed(text.split())))

Answer 6

One version just with loops, without any function:

s = 'Hello  World, this string will be reversed!'

def reverse_words(s):
    rv = ''
    buf = ''
    for ch in s[::-1]:
        if ch != ' ':
            buf += ch
        else:
            if buf:
                rv += buf[::-1] + ' '
            buf = ''
    if buf:
        rv += buf[::-1]

    return rv

s = reverse_words(s)
print(s)

Prints:

reversed! be will string this World, Hello

Answer 7

I started learning python recently and this is something which i tried

name=input("Enter the word you want the reverse :")
a=(len(name))
print(a)
for i in range (1,a+1):

    print("{}".format(name[-i]),end="")