Goto Statement in Python

The goto statement was first activated as a joke on April 1, 2004. Programmers around the world took the goto statement for their programming use, and it’s now one of the essential functions used by every programmer across the globe.

Python is considered to be the most preferred programming language that is technically capable of creating the best operating system in the industry. Everyone starting from the beginners to experts is making use of the Python, but still, few factors are kept unnoticed in Python. One among them is the native goto statement. In this tutorial, let’s check out the native goto statement in Python in a subtle way.

Overview of Goto Statement

A goto statement is termed as the piece of code or syntax that offers an unconditional jump from the goto statement to a labeled statement that is marked as the end in the same function. If I need to explain this in layman terms, let’s say, you need a program to skip some specific number of functions, in this case, a goto statement can be used between the program.

Even though the programmers highly prefer the goto statement, the goto statement lags behind in case of auditing purposes. Yeah, they are weak in tracing the program flow. It’s difficult for the programmers to alter any program content and also to locate the precise destination of the goto statement is tedious. It is because of the goto statement jump from one function to another conveniently.

Let’s check for the syntax of the Goto function in Python.

Syntax-1

Goto label;
..
Label: 
Syntax2
Label:
..
Goto label;

Considering the above syntax, you can replace the label with any text. Let’s admit it as “flow”. So now the syntax will look like

Syntax 1

Goto flow;
..
flow:

Syntax 2

flow:
....
Goto flow;

Goto statement iterations

comefrom is another statement that works identical to the goto function. Both goto and comefrom statements provide flexibility and scalability to the entire Python programs, and this enables one program to control the mechanism of program flow. It also holds the accessibility to control the idioms flow.

The important thing you need to do to make use of both comefrom and goto statement in Python is that you should import them first in the main library. Below is the code to import both comefrom and goto statements in the main library.

From goto import goto, comefrom, label

Once you have imported both goto and comefrom statements, you can make use of these both statements anywhere on your programs conveniently. The main reason for using the goto statement in Python indicates that you are providing instructions to the interpreter to execute the next code line instead of running the present one. ‘Label’ is the section that should be marked by the target line of code, which is the code that the interpreter has executed. The label tags are developed to be random, and they are the arbitrary identifiers in Python that is prefixed by a dot.

For instance, label .mylabel

What do you mean by Computed goto statement in Python?

The computed goto statement is considered to be the common variations used by most of the programmers. In this computed goto statement, you will use the python index in the code beginning and then make use of the hashtag to refer them later. Let’s check out an example.

i = calculateLabelName()
Goto *i

Comefrom

Comefrom in Python is defined just opposite to the goto statement in Python. Its the interpreter functions that can be explained through the statement like, “jump to hear instead, whenever lab ‘a” is reached. Let’s check out an example for the comefrom statement in Python.

#...code a…..
Label .somewhere
#...code b…
comefrom .somehwere

In the above example, the code b will not be executed. The label .somehwere will be skipped and the next line comefrom .somehwere be executed once the interpreter reaches the first line “label .somehwere”.

Comefrom is one of another critical factor that it’s used as a debugging aid when it comes to programming. They are neglected to be used in the standalone programming operations because it has a high chance of leading to supporting and inconvenient results.

What are the restrictions present in the Goto statement in Python?

• Python also has its number of restrictions on comefrom and goto statement as other lines of codes and coding platforms have a one. Here are a few limits for both comefrom and goto statement.
• Programmers will not be able to use both statements at the same time to jump between modules or functions.
• Jumping into the final clause or the middle of any loop is not possible.
• Both goto and comefrom are not possible to be used to jump into an except line as you cannot find an exception line in the first place.

Let’s check out this with an example.

from goto import goto, label
for x in range(1, 10):
for y in range(1, 20):
for z in range(1, 30):
print x,y,z
if z == 3:
goto .end
label .end
print "Finished"

The above example is breaking out from a loop that is deeply nested. Now let’s check out a case that clean up after the fail of something.

from goto import goto, label

# Imagine that these are real worker functions.

def settingUp(): print "settingUp"
def doPrimaryTask(): print 0; return True
def doSecondaryTask(): print 1; return True
def doThirdTask(): print 2; return False # It pretends to fail.
def doFourthTask(): print 3; return True
def cleanUp(): print "cleanUp"

# This prints “settingUp, 0,1,2, cleanUp” – no “3” as doThirdTask fails.

def bigFunction0():
settingUp()
if not doPrimaryTask():
goto .cleanup
if not doSecondaryTask():
goto .cleanup
if not doThirdTask():
goto .cleanup
if not doFourthTask():
goto .cleanup
label .cleanup
cleanUp()
bigFunction0()
print "bigFunction0 done"

The goto statement in Python is considered to be a helpful one for both auditing and debugging purposes. Even though they are used in day to day programming, using the goto statement often can provide you with amazing results.

I hope the above tutorial made you understand about the goto statement in Python clearly. Any doubts regarding the goto or comefrom statement? Let us know through the comment section below.

Related Blogs:

1. Brief Overview of Python Language
2. Python Career opportunities
3. Python Break Continue
4. Python Control Flow
5. Python Data Types
6. Python Dictionary
7. Python Exception Handling
8.  Python File
9. Python Functions
10. Python Substring