Goto Statement in Python: What You Need to Know in 2020

Introduction

Among the plethora of modern programming languages that exist currently, Python is increasingly popular among a large chunk of users. This popularity is mostly owed to the flexibility that it grants to its users by not strictly adhering to traditional syntaxes that its contemporaries do. Consequently, its user-friendliness has resulted in it being a central part of multiple software industries across the globe today. From amateurs to weathered professionals, Python has now become the language of choice for most programmers out there. 

Long-time Python users swear by the diverse range of statements and the subsequently enhanced functionality that it accords them. However, since the number of conventionally used statements is so vast, several equally handy commands go unnoticed as well. One such example is the goto statement in Python. The purpose of this article is to give the readers a greater insight into goto in Python.

Python’s goto statement is an essential piece of code or syntax that enables the user to skip a certain number of statements or a block of code in the program body. In technical terms, it carries out an unconditional jump from the goto statement to the point that is designated as the destination within the context of the same function that is being compiled.

The goto function’s syntax is relatively straightforward for it couples the keyword “goto” with a template label name that can be customized as per the user’s requirement. As long as the text does not consist of the keyword “go”, it can be placed anywhere in the program’s body. It does not make a difference if someone chooses to place the label above the go statement, or for that matter, below it. 

The goto statement as such is widely used by a large chunk of users who program in Python. However, for all its probability, this statement’s use is usually discouraged when auditing purposes are concerned. This is primarily because the presence of a goto statement in an auditing context makes it very difficult for someone to trace the program’s flow.

Consequently, if there ever does arise a situation where a programmer is required to alter any content of the program at any point in time, determining the exact location becomes an uphill task. As the use of the goto statement entails the skipping of a select portion or block of the function, the user finds it difficult to trace the program flow and narrow in on the exact location at which the modification is to be carried out. 

The goto statement has a fun nugget of history attached to it. It is widely believed that when the goto statement was first released, on 1st April 2004, it was supposed to be used as a joke. However, upon realizing the utility of the syntax at hand, programmers started taking the statement seriously. Thus goto gradually grew to enjoy the widespread endorsement that it continues to have to date. 

Goto statement and its iterations

When we talk about an iteration of the goto statement, we are broadly referring to another similar piece of code or syntax that has more or less the same functionality as the goto statement. In the context of Python, these criteria are met by the Comefrom the statement. Comefrom the statement, as a code, works the same way as the goto command works. Both goto and Comefrom’s purpose is to render an added flexibility to the master program as such, which they manage to execute rather conveniently.

As a result, you as a user are accorded greater control over the program flow mechanisms and exercise your liberty within the program’s construct as and when you deem fit. Consequently, it makes way for increased accessibility to varying degrees of the control flow of idioms, which were mostly foreign and virtually out of bounds for the user until this point in time.

To use either of goto or Comefrom statements in a Python program, one first has to import the main library. This is generally achieved by a very straightforward and easy to execute a piece of code which reads as below:

from goto import goto, Comefrom, label

Even though Python does not necessitate memorizing any complicated syntax structures as such, one stands to benefit by a good deal by having codes, like the one mentioned above, at their fingerprints. Implementing commands by importing the main library is core to Python. Thus familiarity with such pieces of code can help save a considerable amount of time for the user in question. Once the libraries are imported into the program’s general body, you can make use of both these commands in your program in a manner that suits you best. 

When one implements the goto statement in Python, there needs to be a basic understanding of what they are achieving by implementing it. This philosophy is not just limited to the context of the goto statement but extends to all such commands within Python. Clarity concerning the functionality of the various commands, apart from helping you optimize the code and run time, also immensely improves the overall program’s readability. This, in turn, directly reflects in your competitive coding skills as such.

In the case of the goto statement, whenever a user invokes it, they are instructing the interpreter to execute a line of code, which is different from the one that is on their hands at that moment. The specific block of the code or the line that you want to target for execution is determined by marking it in the section which is popularly referred to as the “label”. Label tags in Python are increasingly random and are generally viewed as arbitrary python identifiers that are prefixed with a single dot. 

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Computed Goto statement

The computed goto statement is one of the most widely used and common variations of the goto statement that a large number of programmers resort to in Python. While using the computed goto statement, the user is required to mention the python index at the beginning of the program or code. Consequently, the user is supposed to refer to the said index by making use of a hashtag. Essentially what you are doing is assigning the name of a label to a variable during runtime itself and then later referencing it, as and when required, with the help of an asterisk. 

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Comefrom statement

Even though the comefrom statement is widely and popularly considered an iteration of the goto statement in Python, upon closer inspection, one realizes that it actually achieves quite the opposite of what the goto statement does. In layman terms and for the convenience of a general reader, comefrom’s function to the interpreter can be best summarised and understood by the following line:

“Whenever label X is reached, jump to here instead.”

As you can see, because the nature of its functionality is similar to that of the goto statement, in the sense that both allow you to skip certain portions and segments of the code, the comefrom statement is considered by most to be an iteration of the goto command. 

Although the actual working of the comefrom statement is best explained with the help of relevant examples, for the purpose of clarity we shall attempt a brief theoretical explanation. one can assume that with the use of comefrom statement, whenever an interpreter reaches the designated label, it ends up skipping the execution of the subsequent line of code. Instead, it directly jumps to the next label within the body of the program. 

An important point to be noted here is that the use of the comefrom statement is by and large made as a debugging aid in programming. Apart from this, the use of the comefrom statement in the larger context of standalone operations is commonly discouraged. This is primarily because making use of the comefrom statement in such a construct often leads to inconvenient and supporting results. 

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The Goto statement and its restrictions in Python

Most coding platforms generally put a set of restrictions upon the functionalities of commands and other lines of code within their body. In this regard, Python presents no exception, either. It puts a number of restrictions on both the goto statement and its iteration, the comefrom statement. As a result, in the greater scheme of things, both of these commands’ degree of accomplishment remains limited. Some of the most common restrictions that extend to both of these statements are listed below for the ready reference of the future.

  • Even though using the goto command or the comefrom program allows you to skip certain portions and segments of the code, it does not really allow you to jump into the middle of a loop. The final clause in Python is also kept from using either of these statements at any point in time. 
  • At no point in time can the user make active use of the goto or comefrom statements to jump between functions or modules in Python.
  • One can not make use of the goto and comefrom commands to jump into an except line. This is largely because the relevant exception line ceases to exist in the first place. This restriction is largely witnessed when a user has to break out of a deeply nested loop. Alternatively, it is also put to action when there’s a need for cleaning up after something fails. Both of these cases throw ample light upon this particular restriction that Python extends on both the goto as well the comefrom statements. 

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Conclusion

For the purpose of auditing and debugging, the goto statement in Python along with its iteration, the comefrom statement, present themselves as largely feasible and wonderfully accessible options to the user.

Although both of these statements are mostly used quite sparingly in the context of conventional programming, using it more than often, even while taking into consideration the set of restrictions that it has to deal with, can lead to rather surprising results. 

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