Ceremonial magic is a type of magic that depends heavily on book learning; precise, complicated ritual; and intricate sets of correspondences.
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In the West, ceremonial magic was almost entirely rooted in Judeo-Christian myth until the late 19th century. Even today, many ceremonial magicians continue to work within that context. Ceremonial magic is also high magic. It is meant to have a spiritual purpose rather than a practical one, although there could be some overlap in those two concepts.
Historically, folk magic is the magic of the common folk. It has all manner of practical purposes: healing, attracting luck or love, driving away evil forces, finding lost items, bringing good harvests, fertility. Records of these practices are largely non-existent since practitioners were generally illiterate. Rituals were simple and probably evolved over time. They involved everyday items: plant material, coins, nails, wood, and so forth. Folk magic is sometimes called low magic because of its practical nature and because of its association with the lower class.
Witchcraft is a highly problematic term because of the different uses of the word today versus its historical uses. In the West, many magical practitioners are now calling themselves witches and practice a cross between ceremonial magic and folk magic. Workings are generally fairly simple, use common materials, and depend upon emotion and intent rather than exact ritual.
They may also borrow certain practices such as circle casting from ceremonial magic. Historically, however, witchcraft meant malevolent magic, and that is the reason it was persecuted. With no arguments, it will repeat the last line. References to objects may be kept. Calling this magic from clients that do not implement standard input, such as the ipython notebook interface, will reset the namespace without confirmation.
We first fully reset the namespace so your output looks identical to this example for pedagogical reasons; in practice you do not need a full reset:.
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Parameters after the filename are passed as command-line arguments to the program put in sys. It thus sees its environment as if it were being run as a stand-alone program except for sharing global objects such as previously imported modules. Arguments are expanded using shell-like glob match. Unlike real shells, quotation does not suppress expansions. Use two back slashes e.
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To completely disable these expansions, you can use -G flag. On Windows systems, the use of single quotes ' when specifying a file is not supported. Use double quotes ". This is useful if you are experimenting with code written in a text editor which depends on variables defined interactively. This is particularly useful if IPython is being used to run unittests, which always exit with a sys. In such cases you are interested in the output of the test results, not in seeing a traceback of the unittest module.
IPython will give you an estimated CPU time consumption for your script, which under Unix uses the resource module to avoid the wraparound problems of time. Under Unix, an estimate of time spent on system tasks is also given for Windows platforms this is reported as 0. The final timing report will include total and per run results. This allows you to execute your program step by step, watch variables, etc. Internally, what IPython does is similar to calling:. Note that the first breakpoint must be set on a line which actually does something not a comment or docstring for it to stop execution.
When the pdb debugger starts, you will see a Pdb prompt. You can pass other options after -p which affect the behavior of the profiler itself. Similar to the -m option for the python interpreter. Unlike the python interpreter only source modules are allowed no. If -r option is used, the default extension is.
IPython will run the given command using commands. Your command can contain shell wildcards, pipes, etc. Split the output on newlines into a list before assigning it to the given variable. By default the output is stored as a single string. In most cases you should not need to split as a list, because the returned value is a special type of string which can automatically provide its contents either as a list split on newlines or as a space-separated string.
These are convenient, respectively, either for sequential processing or to be passed to a shell command. Similarly, the lists returned by the -l option are also special, in the sense that you can equally invoke the. In summary, both the lists and strings used for output capture have the following special attributes:. Set environment variables. The reason for this is to make it as easy as possible to process line-oriented shell output via further python commands. Optionally, specify an exception reporting mode, tuning the verbosity of the traceback.
By default the currently-active exception mode is used. The CPU and wall clock times are printed, and the value of the expression if any is returned. Note that under Win32, system time is always reported as 0, since it can not be measured. In line mode you can time a single-line statement though multiple ones can be chained with using semicolons.
This function provides very basic timing functionality. Use the timeit magic for more control over the measurement. Time execution of a Python statement or expression using the timeit module. This function can be used both as a line and cell magic:. In cell mode, the statement in the first line is used as setup code executed but not timed and the body of the cell is timed.
The cell body has access to any variables created in the setup code. Default: 7. This function measures wall time. On Unix, resource. Generally, the bias does not matter as long as results from timeit. If any arguments are given, only variables whose type matches one of these are printed. To find the proper type names, simply use type var at a command line to see how python prints type names.
By default, this uses the identity of the named object in the user namespace to remove references held under other names. The object is also removed from the output history. If unspecified, captured output is discarded.
The subset of latex which is support depends on the implementation in the client. Whether you should raise an error message in addition to a stream on stderr if you get a nonzero exit code. Whether to run the script in the background. The variable in which to store stderr from the script. If the script is backgrounded, this will be the stderr pipe , instead of the stderr text itself and will not be autoclosed. The variable in which to store stdout from the script.
If the script is backgrounded, this will be the stdout pipe , instead of the stderr text itself and will not be auto closed. IPython stable. Important This documentation covers IPython versions 6. In : cat? When 0: nothing will be excluded. When True: only those names in obj. In [ 1 ]: edit Editing Executing edited code If I use the number 2 by itself, my first question might be: What does "2" mean?
The meaning of "2" by itself is unknown and unknowable without context, leaving its use unclear and confusing. Even though having just "2" in our software will not happen because of language semantics, we do want to see that "2" by itself carries no special semantics or obvious purpose being alone.
In this context the meaning of 2 as pixels or other graphical unit offers us a quick guess of its semantics meaning and purpose. We might stop here and say that 2 is okay in this context and there is nothing else we need to know. However, perhaps in our software universe this is not the whole story. The notion of "default" is not revealed. The example above is pretty good because "2" by itself could be anything. Thus, any basic value, whose meaning semantic and purpose cannot be sufficiently and quickly understood is a good candidate for a symbolic constant in the place of the basic value e.
Numbers on a scale might have semantics as well. The numbers have meanings that are not knowable or clear without words to supply meaning. Thus, we begin by arbitrarily saying:. Without these words symbolic constants , we are left with just the numbers ranging from Therefore, when searching for and considering replacement of "magic numbers" we want to ask very purpose-filled questions about the numbers within the context of our software and even how the numbers interact semantically with each other.
Examine stand-alone manifest constant basic values in your code text. Ask each question slowly and thoughtfully about each instance of such a value. Consider the strength of your answer. Many times, the answer is not black and white, but has shades of misunderstood meaning and purpose, speed of learning, and speed of comprehension. There is also a need to see how it connects to the software machine around it. In the end, the answer to replacement is answer the measure in your mind of the strength or weakness of the reader to make the connection e.
The more quickly they understand meaning and purpose, the less "magic" you have. A magic number is a sequence of characters at the start of a file format, or protocol exchange. This number serves as a sanity check. The danger is that random binary data can contain these same characters. But it is very unlikely. As for protocol exchange, you can use it to quickly identify that the current 'message' that is being passed to you is corrupted or not valid. In programming, a "magic number" is a value that should be given a symbolic name, but was instead slipped into the code as a literal, usually in more than one place.
It's bad for the same reason SPOT Single Point of Truth is good: If you wanted to change this constant later, you would have to hunt through your code to find every instance. It is also bad because it might not be clear to other programmers what this number represents, hence the "magic". People sometimes take magic number elimination further, by moving these constants into separate files to act as configuration.
This is sometimes helpful, but can also create more complexity than it's worth. If you have very many of them, the odds are reasonably good that you have two different purposes that you're using magic numbers for, where the values happen to be the same. A magic number can also be a number with special, hardcoded semantics. What's bad about this is that you're reusing a space that of signed integers for record IDs for special abilities.
Maybe you'll never want to create a record with ID 0, or with a negative ID, but even if not, every person who looks either at the code or at the database might stumble on this and be confused at first. It goes without saying those special values weren't well-documented. Arguably, 22, 7, and count as magic numbers, too. I assume this is a response to my answer to your earlier question. In programming, a magic number is an embedded numerical constant that appears without explanation.
If it appears in two distinct locations, it can lead to circumstances where one instance is changed and not another. For both these reasons, it's important to isolate and define the numerical constants outside the places where they're used. It is worth noting that sometimes you do want non-configurable "hard-coded" numbers in your code. There are a number of famous ones including 0x5FDF which is used in the optimized inverse square root algorithm.
In the rare cases where I find the need to use such Magic Numbers, I set them as a const in my code, and document why they are used, how they work, and where they came from. I've always used the term "magic number" differently, as an obscure value stored within a data structure which can be verified as a quick validity check. For example gzip files contain 0x1f8b08 as their first three bytes, Java class files start with 0xcafebabe, etc.
You often see magic numbers embedded in file formats, because files can be sent around rather promiscuously and lose any metadata about how they were created. However magic numbers are also sometimes used for in-memory data structures, like ioctl calls. A quick check of the magic number before processing the file or data structure allows one to signal errors early, rather than schlep all the way through potentially lengthy processing in order to announce that the input was complete balderdash. In this case, is a magic number according to CheckStyles. To me, setting a default value is okay.
I don't want to have to do:. A principle that's related to magic numbers is that every fact your code deals with should be declared exactly once. If you use magic numbers in your code such as the password length example that marcio gave, you can easily end up duplicating that fact, and when your understand of that fact changes you've got a maintenance problem.
It return the Id of the company if it exists in a particular table. Otherwise, it returns Somehow it's a magic number. Some of the recommendations I've read so far says that I'll really have to do design somthing like that:. By the way, what should it return if the company does not exists? Ok: it will set existesCompany as false , but also will return The bottom line by the way is: what do you think about using that kind of "magic numbers" that are relatively known and safe to tell that something is unsuccessful or that something does not exists?
Another advantage of extracting a magic number as a constant gives the possibility to clearly document the business information. What is a magic number, and why is it bad?
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