Learn Python - Full Course for Beginners [Tutorial]
For applications that require data compression, the functions in this module allow compression and decompression, using the zlib library. There are known incompatibilities between the Python module and versions of the zlib library earlier than 1. For reading and writing. For other archive formats, see the bz2zipfileand tarfile modules.
Computes a Adler checksum of data. An Adler checksum is almost as reliable as a CRC32 but can be computed much more quickly. If value is present, it is used as the starting value of the checksum; otherwise, a fixed default value is used. This allows computing a running checksum over the concatenation of several inputs.
The algorithm is not cryptographically strong, and should not be used for authentication or digital signatures. Since the algorithm is designed for use as a checksum algorithm, it is not suitable for use as a general hash algorithm. If you are only using the checksum in packed binary format this is not necessary as the return value is the correct 32bit binary representation regardless of sign.
Changed in version 2. In older versions the value is signed on some platforms and unsigned on others. Changed in version 3. In older versions the value would be signed on some platforms and unsigned on others. Decompresses the data in stringreturning a string containing the uncompressed data. The wbits parameter controls the size of the window buffer, and is discussed further below. If bufsize is given, it is used as the initial size of the output buffer.
Raises the error exception if any error occurs. Its absolute value should be between 8 and 15 for the most recent versions of the zlib library, larger values resulting in better compression at the expense of greater memory usage. When decompressing a stream, wbits must not be smaller than the size originally used to compress the stream; using a too-small value will result in an exception.
The default value is therefore the highest value, When wbits is negative, the standard gzip header is suppressed. The default size is Returns a copy of the compression object.
This can be used to efficiently compress a set of data that share a common initial prefix. A string which contains any bytes past the end of the compressed data. That is, this remains "" until the last byte that contains compression data is available. If the whole string turned out to contain compressed data, this is ""the empty string. The only way to determine where a string of compressed data ends is by actually decompressing it.
Decompress stringreturning a string containing the uncompressed data corresponding to at least part of the data in string. This data should be concatenated to the output produced by any preceding calls to the decompress method. Some of the input data may be preserved in internal buffers for later processing. This string must be passed to a subsequent call to decompress if decompression is to continue. All pending input is processed, and a string containing the remaining uncompressed output is returned.The zlib compression format is free to use, and is not covered by any patent, so you can safely use it in commercial products as well.
It is a lossless compression format which means you don't lose any data between compression and decompressionand has the advantage of being portable across different platforms. Another important benefit of this compression mechanism is that it doesn't expand the data. The main use of the zlib library is in applications that require compression and decompression of arbitrary data, whether it be a string, structured in-memory content, or files.
The most important functionalities included in this library are compression and decompression. Compression and decompression can both be done as a one-off operations, or by splitting the data into chunks like you'd seem from a stream of data. Both modes of operation are explained in this article.
The zlib library provides us with the compress function, which can be used to compress a string of data. The syntax of this function is very simple, taking only two arguments:. Here the argument data contains the bytes to be compressed, and level is an integer value that can take the values -1 or 0 to 9. This parameter determines the level of compression, where level 1 is the fastest and yields the lowest level of compression.
Level 9 is the slowest, yet it yields the highest level of compression. The value -1 represents the default, which is level 6. The default value has a balance between speed and compression. Level 0 yields no compression. You may notice a few differences comparing the outputs when using 0 or 2 for the compression level.
Using a level of 2 we get a string formatted in hexadecimal of length 38, whereas with a level of 0 we get a hex string with length This difference in length is due to the lack of compression in using level 0.
If you don't format the string as hexadecimal, as I've done in this example, and view the output data you'll probably notice that the input string is still readable even after being "compressed", although it has a few extra formatting characters around it. Large data streams can be managed with the compressobj function, which returns a compression object.
The syntax is as follows:. The main difference between the arguments of this function and the compress function is aside from the data parameter the wbits argument, which controls the window size, and whether or not the header and trailer are included in the output. The method argument represents the compression algorithm used. The strategy argument relates to compression tuning. Unless you really know what you're doing I'd recommend to not use it and just use the default value.
As we can see from the figure above, the phrase "Hello world" has been compressed. Typically this method is used for compressing data streams that won't fit into memory at once. Although this example does not have a very large stream of data, it serves the purpose of showing the mechanics of the compressobj function. This can then be used to compress chunks of data in series.
You may also be able to see how it would be useful in a scenario where you have a data stream to compress. Instead of having to accumulate all of the data in memory, you can just call compress. We can also use the compress function to compress the data in a file.This function is the primary interface to this module along with decompress function. This function returns byte object by compressing the data given to it as parameter.
The function has another parameter called level which controls the extent of compression. It an integer between 0 to 9. Lowest value 0 stands for no compression and 9 stands for best compression. Higher the level of compression, greater the length of compressed byte object.
This function does the opposite of compress function. It retrieves the uncompressed data. This function can have an optional parameter called wbits which controls the size of history buffer and the nature of header and trailer format. The module consists of definitions of has two corresponding classes of compression and decompression objects.
Two important method of this object are. This method empties the buffer. Following example sets up compression object and constructs a compressed data object by adding the flushed data to the return value of compress method.
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I need to create a function called compress that compresses a string by replacing any repeated letters with a letter and number. Can someone suggest a better way to do this?
This will allow you to test it more easily. You will also be able to return values instead of printing them, this will make the code more reusable:. Counter offers simplified ways of counting elements of an iterable:. You can even simplify further as Counter can take any iterable in its constructor. You can also use str. To me, compressing a string mean having a mean to decompress it back. Using a dictionnary keyed by each letter as you do, you lost an important information: which letter is next to which one.
Also 'aabaabaabaa' will be compressed to 'a8b3' which, to me, doesn't make sense and would be better as 'a2b1a2b1a2b1a2'.
But I might be wrong. In this case, itertools. In the itertools module there is the groupby function that groups together runs of the same values. It also has the advantage that it directly iterates over the input, instead of over its indices have a look at Loop like a Native!
This makes it work also for a generator, which does not have a length:. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. String compression function in python code [closed] Ask Question. Asked 1 year, 3 months ago. Active 9 months ago. Viewed 8k times. Peilonrayz Active Oldest Votes.
But if you find a nice way to write it as a comprehension that would be nice, I could not think of any. But I only have 3. This makes it work also for a generator, which does not have a length: from itertools import islice, cycle compress islice cycle 'a'10 'a10'. Graipher Graipher Please explain your reasoning how your solution works and why it is better than the original so that the author and other readers can learn from your thought process.
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Compression compatible with gzip in Python (zlib)
Community and Moderator guidelines for escalating issues via new response….A compressed file is a sort of archive that contains one or more files that have been reduced in size. Compressing files in modern operating systems is usually pretty simple.
However, in this tutorial, you will learn how to compress and decompress files using Python programming language. You may ask, why would I learn to compress files in Python where there are already provided tools out there? Well, de compressing files programmatically without any manual clicks is extremely useful, for example, when downloading machine learning datasets in which you want a piece of code to download, extract and load them into memory automatically. Let's get started, we will be using tarfile built-in module, so we don't have to install anything, you can optionally install tqdm just for printing progress bars:.
Open up a new Python file and:. I've optionally wrapped members with tqdm to print progress bars, this will be useful when compressing a lot of files in one go. That's it for compression, now let's dive into decompression. The below function is for decompressing a given archive file:. First, we opened the archive file as reading with gzip compression.
After that, I made a optional parameter 'member' in case we want to extract specific files not all archiveif 'members' isn't specified, we gonna get all files in the archive using getmembers method which returns all the members of the archive as a Python list. And then for each member, extract it using extract method which extracts a member from the archive to the 'path' directory we specified.
Note that we can alternatively use extractall for that which is prefered in the official documentation. Let's test this:. This will compress test. If you want to decompress:. This will decompress the previous archive we just compressed to a new folder called extracted:. Okey, we are done! You can be creative with this, here are some ideas:. In this tutorial, we have explored compression and decompression using tarfile module, you can also use zipfile module to work with ZIP archives, bz2 module for bzip2 compressions, gzip or zlib modules for gzip files.
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Sign in. Compress and decompress string in Python. Please write a program to compress and decompress the string. Which module should be used?
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Your comment on this answer: Your name to display optional : Email me at this address if a comment is added after mine: Email me if a comment is added after mine Privacy: Your email address will only be used for sending these notifications. Related Questions In Python. How can I print variable and string on same line in Python? Is it possible to print a string and a variable in a single print statement in Python? Lowercase in Python You can simply the built-in function in Python: Print variable and string in same line For a better understanding you can refer Welcome back to the World's most active Tech Community!
Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. On my serverside, I used zlib python library to compress zlib. In my redis, it shows:. If I read it from redis to python and use python zlib. It can print "Hello World". What should I in order to decompress it? Is there any performance difference? Pretty late, but today I found myself working on exactly the same problem. I manage to solve it like this:.
Java code decompressI'm using Java 8 so we have a built in base64 decoder, for other java versions there are plenty of decoders out there. Also to keep things short, I didn't put the exception handling code:.
Learn more. Asked 4 years, 4 months ago. Active 3 years, 11 months ago. Viewed 8k times. How can I do it in java? I tried this piece of code from Java 7 official documents. DataFormatException: incorrect header check What should I in order to decompress it? Sean Sean 77 2 2 silver badges 6 6 bronze badges. Did you ever solve this? I'm in the same predicament Active Oldest Votes. Sign up or log in Sign up using Google.
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