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Consider a String a f-string in Python

Suppose I have
x = 3
s = "f'12{x}4'"
How to consider s as f-string to print 1234, like writing print(f'12{x}4')
when I print s, it prints it as it as: f'12{x}4'

Remve the double quotations that should fix the issue because the f in a f string needs to be outside the actuall string

You are missing two concepts.
The first one, is how you tell python your string is an f-string. The way to do this, is by adding the character 'f' before the first quotation mark:
f"this will be a f-string"
Whatever you have between {}, it will be a previously defined variable:
x = "something"
f"this will be {x}"

Assuming you ask this because you can not use actual f-strings, but also don't want to pass the parameters explicitly using format, maybe because you do not know which parameter are in the not-really-an-f-string, and also assuming you don't want to use eval, because, well, eval.
You could pass the variables in the locals or globals scope to format:
>>> x = 3
>>> s = '12{x}4'
>>> s.format(**globals())
'1234'
>>> s.format(**locals())
'1234'
Depending on where s is coming from (user input perhaps?) This might still be a bit risky, though, and it might be better to define a dict of "allowed" variables and use that in format. As with globals and locals, any unused variables do not matter.
>>> vars = {"x": x, "y": y, "z": z}
>>> s.format(**vars)
Note that this does not give you the full power of f-strings, though, which will also evaluate expressions. For instance, the above will not work for s = '12{x*x}4'.

You'd do this -
x = 3
s = f'12{x}4'

This can also work.
x = 3
s = "12{}4"
print(s.format(x))

Just remove extra commas
s = f'12{x}4'

x = 3
s = '12{}4'.format(x)
or
x = 3
print('12%s4' %x)

How to get input from multiple lines?

i want to take input from user in and each value of the input is on consecutive line.this is to be implemented in python
while x=int(raw_input()): ##<=showing error at this line
print(x)
gollum(x)
#the function gollum() has to be called if the input is present

The reason why your code does not work is why wants a condition or an object. As you are assigning a value (x=raw_input()), while does not find anything to test (an assignment does NOT return any value).
You can either request an input, and then do a while loop depending on the value of this input (that will be modified inside the while loop) :
x = int(raw_input())
while x:
print(x)
gollum(x)
x = int(raw_input())

That gives you an error because x=int(raw_input()) doesn't return a boolean, and you need a boolean inside the while condition.
You can try this one:
while True:
x = raw_input()
if x=='':
break
x = int(x)
print(x)
gollum(x)
that way if you put an empty string (just an enter) the program just stops and doesn't give an annoying error :P

How to complete this function then print it out, using Python?

I'm having a hard time to understand how to work with functions - I can make then but after that I don't know how to use them. My question is how can I print this code with a function?
string = "Hello"
reverse = string[::-1]
print(reverse)
I tried putting it in a function but I cannot make it print Hello.
def reverse_a_string(string):
string = "Hello"
reverse = string[::-1]
print(reverse)
also tried this
def reverse_a_string(string):
string = "Hello"
reverse = string[::-1]
print(reverse)
Nothing seems to work. I'm having same problem with this as well.
total = 0
def length(words):
for i in words:
total += 1
return total

Functions without a return value
Functions that just take action or do something without returning a value (for example, print).
Functions that don't return a value can be defined like that:
def sayHello():
print "Hello!"
And can be used (called) like that:
sayHello()
And the output will be:
Hello!
Function parameters
A function can also receive parameters (type of variables) from the caller. It's better to demonstrate it with an example.
A function that receives a name and greets this name:
def sayHelloTo(name):
print "Hello", name
It can be called like that:
sayHelloTo("Yotam")
And the output will be:
Hello Yotam
The parameters are the function's input.
Functions with a return value
Other functions, unlike sayHello() or sayHelloTo(name) (that just do something) can return a value. For example, let's make a function that rolls a dice (returns a random number between 1 and 6).
from random import randint
def rollDice():
result = randint(1, 6)
return result
The return keyword just sets the output value of the function and exits the function. An example use of the rollDice function will be:
dice = rollDice()
print "The dice says", dice
When the function hits a return keyword, it finishes and the return value (in our case, the variable result) will be placed instead of the function call. Let's assume randint(1, 6) has produced the number 3.
Result becomes 3.
Result is returned.
Now, instead of the line:
dice = rollDice()
We can treat the line as:
dice = 3
(rollDice() was replaced with 3)
Functions with parameters and a return value
Some functions (for example, math functions) can take inputs AND produce outputs. For example, let's make a function that receives 2 numbers and outputs the greater one.
def max(a,b):
if a > b:
return a
else:
return b
What it does is pretty clear, isn't it? If a is greater, it returns the value of it. Otherwise, returns the value of b.
It can be used like that:
print max(4, 6)
And the output will be:
6
Now, your case
What you want to do is a function that reverses a string. It should take 1 parameter (input) - the string you want to reverse, and output 1 value - the reversed string. This can be accomplished like that:
def reverse_a_string(my_text):
return my_text[::-1]
now you can do something like that:
s = raw_input("Please enter a string to be reversed\n") #input in Python3
r = reverse_a_string(s)
print r
r will contain the reversed value of s, and will be printed.
About your second function - well, I assume that based on this answer you can make it yourself, but comment me if you need assistance with the second one.
Local variables
About your 3rd example:
def reverse_a_string(string):
string = "Hello"
reverse = string[::-1]
print(reverse)
This is something that is really worth delaying and understanding.
the variable reverse is first used inside the function. This makes it a local variable.
This means that the variable is stored in the memory when the function is called, and when it finishes, it is removed. You can say it's lifetime is from when the function is called to when the function is done.
This means that even if you called reverse_a_string(string), you wouln't be able to use the reverse variable outside of the function, because it would be local.
If you do want to pass a value like that, you have to "declare" your variable outside of the function and to use the global keyword, like that:
reverse = "" #This makes reverse a global variable
def reverse_a_string(string):
global reverse #Stating that we are going to use the global variable reverse
reverse = string[::-1]
# Then you can call it like that:
reverse_a_string("Hello")
print reverse
The output will be
olleH
Although it's strongly not recommended to do it in Python, or in any other language.

Once you create a function you must call it. You have created the function reverse_a_string but then you never actually call it. Think about a function as a button that does something everytime it is pushed (or in our case called). If you never push the button then although it has the potential to do something, it never will. In order for the set of instructions to happen we need to push the button (or in our case call the function). So in order for your code to work you first need to define the function then actually call it:
def reverse_a_string():
string="Hello"
reverse = string[::-1]
print reverse
reverse_a_string()
Result: 'olleH'
If you want to pass your own string in to the function so it doesn't just return 'olleH' all the time your code needs to look like such:
def reverse_a_string(stringThatWillBeReversed):
reverse = stringThatWillBeReversed[::-1]
print reverse
reverse_a_string('whateverStringYouWant')
Result: The reverse of the string you entered.
Hope that helps!

I don't know whether you are asking how to define functions in python or something else
If you want to learn python functions, go to http://www.tutorialspoint.com/python/python_functions.htm or just write python tutorial in google, you will get billions of good sites
def reverse_a_string(string):
#function definition
reverse = string[::-1]
print(reverse)
#function call
reverse_a_string("your string")
But you to define function for this, you could simply do
print( string[::-1] )

# defines the 'Reverse a String' function and its arguments
def reverse_a_string():
print(string)
reverse = string[::-1]
print(reverse)
print("Type a string") # asks the user for a string input
string = input() # assigns whatever the user input to the string variable
reverse_a_string() # simply calls the function
for functions, you have to define the function, then simply call it with the function name i.e. funtion()
In my example, I ask for a string, assign that to the variable, and use it within the function. If you just want to print hello (I'm a little unclear from your question) then simply including the print("hello") or w/ variable print(string) will work inside the function as well.

How do I access the string inside my function python?

Trying to gain access to this string to test it if it has 3 or more blues "b" inside of it. ---Both test and three_or_more_blues are functions.----- I'm completely lost, any one got an idea? Please change my title if it doesn't fit my question. Not sure really how to ask the question. Thanks!
test(three_or_more_blues, "brrrrrbrrrrrb")

Assuming test is a function that takes a function and a string as paramters, and three_or_more_blues is a function that returns true if its string parameter has 3 or more 'b' characters, then
def test(func, str):
if func(str):
# do something with str
test(three_or_more_blues, "brrrrrbrrrrrb")

You could use .count().
sentence = 'brrrrrbrrrrrb'
amount = sentence.count('b')
print(amount)
And then you could use a loop to calculate your next step.
if (amount >= 3):
# Do something

I am not sure if I understand you correctly - you are asking how to pass the string 'brrrrrbrrrrrb' to the three_or_more_blues function?
If that is the case, than you just simply pass it when you call the three_or_more_blues function like this:
def test(func, some_string):
func(some_string) # here you call the passed function
# if three_or_more_blues would look like this:
def three_or_more_blues(some_string):
print "Yes, 3 or more b's" if some_string.count('b') >= 0 else "No"
# you would get this from your function call
test(three_or_more_blues, "brrrrrbrrrrrb") # prints: "Yes, 3 or more b's"

Using a variable outside of function in Python

A really simple question, and I'm sure I knew it but must have forgotten
When running this code:
x = 0
def run_5():
print "5 minutes later"
x += 5
print x, "minutes since start"
run_5()
print x
I get x isn't defined. How can I have x used in the function and effected outside of it?

Just return a value ?
x = 0
def run_5():
print "5 minutes later"
x += 5
return x
x=run_5()
print x

Put global x at the start of the function.
However, you should consider if you really need this - it would be better to return the value from the function.

Just to make sure, the x that is not defined is the one on line 4, not the one on the last line.
The x outside the function is still there and unaffected. It's the one inside that can't have anything added to it because, as far as Python is concerned, it does not exist when you try to apply the += operator to it.

I think you need to define a variable outside the function, if you want to assign it a return value from the function.
The name of the variable can be different than the name in function as it is just holding it