File validation in python

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If nothing happens, download GitHub Desktop and try again. If nothing happens, download Xcode and try again. If nothing happens, download the GitHub extension for Visual Studio and try again. A simple Python library containing functions that check Python values. It is intended to make it easy to verify commonly expected pre-conditions on arguments to functions. Originally developed and open-sourced at Joivy Ltd.

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The validation library is available on PyPI. As this library is a useful tool for cleaning up established codebases, it will continue to support Python 2. The string validation functions are particularly handy for sorting out unicode issues in preparation for making the jump to Python 3.

The validation functions provided by this library are intended to be used at the head of public functions to check their arguments. Exceptions raised by the validation functions are allowed to propagate through. Everything is inline, with no separate schema object or function.

This library contains a number of functions that will check their first argument if one is provided, or return a closure that can be used later. Functions check values against a semantic type, not a concrete type.

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Functions are fairly strict by default. Intended to be mixed with normal Python code to perform more complex validation. As an example, the library provides no tools to assert that to values are mutually exclusive as this requirement is much more clearly expressed with a simple if block. The validation library is not a schema definition language.

Validation functions and closures are not designed to be introspectable, and are expected to be used inline.When it comes to data, no one really knows what a large database contains. Python can help data scientists with that issue. You must validate your data before you use it to ensure that the data is at least close to what you expect it to be. What validation does is ensure that you can perform an analysis of the data and reasonably expect that analysis to succeed. Later, you need to perform additional massaging of the data to obtain the sort of results that you need in order to perform your task.

Spending more computational time to process duplicates, which slows your algorithms down. Obtaining false results because duplicates implicitly overweight the results. Because some entries appear more than once, the algorithm considers these entries more important.

file validation in python

This example shows how to find duplicate rows. It relies on a modified version of the XMLData. A real data file contains thousands or more of records and possibly hundreds of repeats, but this simple example does the job.

The example begins by reading the data file into memory. It then places the data into a DataFrame. At this point, your data is corrupted because it contains a duplicate row.

However, you can get rid of the duplicated row by searching for it. The first task is to create a search object containing a list of duplicated rows by calling pd.

The duplicated rows contain a True next to their row number. Following is the output you see from this example. Notice that row 1 is duplicated in the DataFrame output and that row 1 is also called out in the search results:. To get a clean dataset, you want to remove the duplicates from it. Fortunately, pandas does it for you, as shown in the following example:.

As with the previous example, you begin by creating a DataFrame that contains the duplicate record.Prerequisites : Django Installation Introduction to Django. Django works on a MVC pattern. So there is a need to create data models or tables. For every table a model class is created. Some of the advantages of a MVC framework are listed out here. Suppose there is a form which takes Usernamegender and text as input from user, the task is to validate the data and save it. After creating the data models, the changes need to be reflected in the database to do this run the following command:.

Later run the command given below to finally reflect the changes saved onto the migration file onto the database. Now a form can be created.

file validation in python

Suppose that the username length should not be less than 5 and post length should be greater than Then we define the Class PostForm with the required validation rules as follows:. Till now, the data models and the Form class are defined.

Now the focus will be on how these modules, defined above, are actually used. If a form with username of length less than 5 is submitted, it gives an error at the time of submission and similarly for the Post Text filled as well. The following image shows how the form behaves on submitting in valid form data. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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How to Validate Your Data with Python for Data Science

Writing code in comment? Please use ide. In django this can be done, as follows:. Model :. Male, 'Male'. FeMale, 'Female'. This is used to write a post. Values for gender are restricted by giving choices.When we accept user input we need to check that it is valid.

This checks to see that it is the sort of data we were expecting. There are two different ways we can check whether data is valid. Method 1: Use a flag variable.

This will initially be set to False. If we establish that we have the correct input then we set the flag to True. We can now use the flag to determine what we do next for instance, we might repeat some code, or use the flag in an if statement.

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Here, we try to run a section of code. This example is fine for checking integers, but will not check floating point numbers or negative numbers. You can reuse this function in your own code as an easy way to get an integer from a user. Easy Python Docs 3. Output Input Comments Variables Strings operations Arithmetic and mathematics Comparison and logical operators Data types and conversions For loops If statements While loops Lists Arrays Procedures Functions File handling Random numbers Validation Definition Easy example Syntax Using a flag Using an exception Examples Example 1 - Check if input contains digits using a flag Example 2 - A range and type check using a flag and exception Example 3 - A length check using a flag Example 4 - Multiple validations using a flag Example 5 - Check for a float using an exception Example 6 - A function to get an integer from the user Example 7 - A function to get a floating point number from the user Key points SQL Extras.

Types of validation: Validation technique Meaning Type check Checking the data type e. Length check Checking the length of a string Range check Checking if a number entered is between two numbers.

How old are you? Note This example is fine for checking integers, but will not check floating point numbers or negative numbers. Enter password at least 5 characters: asdf Password entered is too short Enter password at least 5 characters: Password entered is too short Enter password at least 5 characters: ad4fgj Your password entered is: ad4fgj. What is your height in cm? What is your age?

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Note You can reuse this function in your own code as an easy way to get an integer from a user. How tall are you?Testing is, to be honest, the typical developers least favorite phase in the development cycle, and data validation is probably the worst part of it. Even simple outbound integrations can require a great deal of tedious, time consuming file auditing. Suppose you need to extract a value from a certain position in a fixed width file, or from a certain column in a delimited file, and compare it to report data.

For a one-off validation, you can do this with excel's text import tool, but in most cases you'll have to repeat the import process with each new file.

Fortunately, Python has a few pre-built libraries and tools that make text file parsing relatively easy. If you're willing to open a text editor and do a bit of scripting, you can create a reusable tool for reading and validating file data. This is also a great way to spur Python uptake in your organization.

file validation in python

Just sayin'. Oh, and your favorite text editor.

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Once that's done, all you'll need to do to execute a program is save your code file a. Lets look at the first few lines of a typical script: import sys import re import struct for line in open sys. Read only 'r' is sufficient for my purposes. As for the file name, I could hardcode a path, but I'd like to be able to specify the file to read at run time, so I'm going to make use of a built in list of variables in the supplied 'sys' package called 'argv' short for 'argument vector' that refer to the arguments passed to the python executable.

To import the sys package we just include this line at the top of our script: import sys and any functions and variables in that package are now available to us We've done this with a couple other packages, and I'll explain what we're doing with them below.

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As I mentioned, we're going to take the argument list and read the second value into the file name the first is the name of the script. In addition, the open function returns a 'file handle' object which can be used to keep track of our position in the file as we read. A particulary cool feature is that we can treat this file handle object as a list, and loop through each line of the file as follows: for line in open sys.

If you need a richer feature set, the csv module offers support for quote escaping, reading into Dictionary objects, and the like. Let's take a look at a practical example. I'm sure some of you will recognize this type of file right away, and groan: For the uninitiated, this is what an ADP PSS file looks like - A file-level header, followed by up to around 30 per-worker lines, and one or two file trailer records. Yes, it's completely anonymized.

While the lines themselves are fixed-width, but the number of lines for each payment can vary based on a number of factors your tenants payroll setup, the number of lines on the paystub, etc. The best strategy here is to look for the specific lines contining the data you're interested in based on the line record ID in the first six characters of the line, and then read the data at specific positions in the line based on the ADP provided file specification.

There's a larger demo script available here. Seriously, unit testing is painful and time consuming and with an approach like this you can 1. I want to also note that there is a package for analytics called 'pandas' available, which allows for almost SQL-like aggregations on data sets once they've been read into standard structures. As I write this, the functionality for reading fixed-width files is still pretty new and probably doesn't have the flexibility you need yet though it reads csv files beautifully.

In time I may update this post with an alternate approach. Stay tuned.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I am working on a project for work that involves the parsing of a file for insertion into our local database. In an effort to write efficient robust code I am trying to see what the best approach is for validating the file.

I have written two python scripts:. As I hope is obvious, I am using simple string literal comparisons with various formatting done to ensure some safety, as well as a version that relies purely on regex's.

Could anyone explain the pros and cons of these two approaches? They both take the same amount of time to execute and are both fairly readable. The only advantage I can see so far is that using regex's means not having to do so much manual formatting prior to comparing string literals.

Assuming you don't see a problem of loading the whole file, and assuming you fix your regex the way you presented it the program would break on non-match, you should check if there was a match, not if there is a group within it those two are not the same. Consider the first line of your file being:. Your regex 'validator' will mark it successful, your string compare won't.

file validation in python

Also, your regex 'validator' will consume all the whitespace characters in the 'replacement' part including tabs, which your string comparator won't. All things being equal - string search will be considerably faster in both cases - and that is not counting loading of the regex engine, preparing the patterns and all other supporting structures needed.

Even if you cache the pattern, and remove all of the disadvantages of regex, string compare will still be faster.

How to Validate Your Data with Python for Data Science

Consider a setup like:. This would cover both cases strict and matching the beginning only with both approaches. You weren't considering building your regex pattern to ignore whitespace so you wouldn't need substitution, but it wouldn't speed it up considerably actually, it will probably run slower than this.

So now if you have 3 files, say good. And if you time the calls for each of those so 3 calls, with 3 different lines per loop over, say,loops you get:.Continuing my post series on the tools I use these days in Python, this time I would like to talk about a library I really like, named voluptuous.

It's no secret that most of the time, when a program receives data from the outside, it's a big deal to handle it. Indeed, most of the time your program has no guarantee that the stream is valid and that it contains what is expected.

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The robustness principle says you should be liberal in what you accept, though that is not always a good idea neither. Whatever policy you chose, you need to process those data and implement a policy that will work — lax or not. That means that the program need to look into the data received, check that it finds everything it needs, complete what might be missing e. The first step is to validate the data, which means checking all the fields are there and all the types are right or understandable parseable.

Voluptuous provides a single interface for all that called a Schema. The argument to voluptuous. Schema should be the data structure that you expect. Voluptuous accepts any kind of data structure, so it could also be a simple string or an array of dict of array of integer.

You get it. Here it's a dict with a few keys that if present should be validated as certain types. By default, Voluptuous does not raise an error if some keys are missing. However, it is invalid to have extra keys in a dict by default. If you want to allow extra keys, it is possible to specify it.

You can create custom data type very easily. Voluptuous data types are actually just functions that are called with one argument, the value, and that should either return the value or raise an Invalid or ValueError exception. Most of the time though, there is no need to create your own data types.

Voluptuous provides logical operators that can, combined with a few others provided primitives such as voluptuous. Length or voluptuous. Rangecreate a large range of validation scheme. The voluptuous documentation has a good set of examples that you can check to have a good overview of what you can do. What's important to remember, is that each data type that you use is a function that is called and returns a value, if the value is considered valid.

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That value returned is what is actually used and returned after the schema validation:. Note a little trick here: it's not possible to use directly uuid. UUID in the schema, otherwise Voluptuous would check that the data is actually an instance of uuid. UUID :. So far, Voluptuous has one limitation so far: the ability to have recursive schemas. The simplest way to circumvent it is by using another function as an indirection.

So far it has been a really good tool, and we've been able to create a complete REST API that is very easy to validate on the server side. I would definitely recommend it for that.

It blends with any Web framework easily. One of the upside compared to solution like JSON Schemais the ability to create or re-use your own custom data types while converting values at validation time. It is also very Pythonic, and extensible — it's pretty great to use for all of that. It's also not tied to any serialization format.

That makes it easy to be exported and provided to a consumer so it can understand the API and validate the data potentially on its side. Data validation The first step is to validate the data, which means checking all the fields are there and all the types are right or understandable parseable. MultipleInvalid: extra keys not allowed data['unknown'] The argument to voluptuous. MultipleInvalid: required key not provided data['foo'] You can create custom data type very easily.