# Javascript Power Function

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The operator ** and the pow () function calculate the power of a number in Python. The operator ** increases the number on the left to the power of the number on the right. The pow () function raises the first parameter to the power of the second parameter.

Calculating the power of a number is a common mathematical operation. For example, if you are creating a program that helps students in a sixth grade math class review powers, you will need a power function.

## Python Power

In Python programming, the power of a number can be calculated in two ways: using the ** operator and using the pow () function.

This tutorial will explain how to use these two techniques to calculate the power of a number. We will see an example of using both the ** operator and the pow () method.

## Python Power: ** Operator

The Python ** The is used to raise a number in Python to the power of an exponent. In other words, ** is the power operator in Python.

The ** operator requires two values ‚Äã‚Äãto perform a calculation. Here is the syntax of the ** operator:

Our program returns the following result: 25.

In this expression, 5 is the second high power. Or, in other words, the number 5 is multiplied by itself 3.

### Python ** Example operator

Let’s take an example to show how the ** operator can be used in Python. Let’s say we create an app that tests sixth grade math students on their knowledge of powers.

To do this, we want to present a student with a math problem, so we want to ask them for the answer. Our program will then calculate the answer to the problem and compare it with the answer the user entered into the program.

Here is an example of a program that would allow us to test sixth graders in math on their knowledge of powers:

When we run our program and insert the answer 56, we get the following answer:

As you can see, our program calculated that our answer was incorrect and returned a message with the correct answer.

In the first line we declare a variable called number which stores the number we want to raise to mathematical power. Then, we declare exponent which is the number of the exponent to which we will raise the variable number.

On the next line, we use Python input () method to ask the user: how much is 7 to the power of 2?

We use Python data type int () conversion method to convert the user’s response to an integer. This is necessary because input () returns a string and we can only use the ** operator with numbers.

Next, we calculate the answer to the question using the ** operator. In this case, we use 7 ** 2 to calculate 7 to the power of 2.

We declare an if statement that prints the message " You’re right! ‚" to the console. If a user gets the correct answer and prints a message with the correct answer if a user is incorrect.

## Power Python: pow () method

Python includes a built-in function that can be used to calculate powers: pow (). pow () takes three parameters: a base number, an exponent to which the base is high and a modulus operator.

The pow () method calculates a number to the power of another number. First, the method converts its argument to a floating point number. Then she calculates the power.

Here is the syntax of the Python pow () method:

The pow () method accepts three parameters:

• base is the number raised to the power of the exponent (mandatory)
• exponent is the number corresponding to the high base (mandatory)
• modulo performs a modulo calculation on the result of the base exponent **. If modulo is specified, the base and exponent must be integers and the exponent must be a positive value. (optional)

If the first two arguments are specified, the base declared to the power of the exponent is calculated.

If the third argument is also specified, the base declared to the power of the exponent is calculated. Then, pow () returns the form of the calculated number. This is a more advanced feature with specific use cases, so we won’t cover it in detail in this article.

To learn more about the Python module operator, read our Python Module Operator’s Guide .

### Python pow () method example

Let’s use our example above to explain how the pow () works. Let’s say we create a game to test their math knowledge.

Our program asks a user for an answer to a question and calculates the answer. Next, our code compares whether the user’s response is the same as the one calculated by the program.

Instead of using the ** operator, we could use pow () to calculate the power of numbers in our code. Here is an example of pow () used with the code we used for our sixth grade power play:

Our code is similar to the first example with one difference. Instead of declaring answer = 7 ** 2, we assign the value pow (7, 2) to the variable answer. If we put the answer 49 in our code, the program returns:

## Conclusion

The ** operator and the pow () method raise a number to the power of another number. These are the advanced methods of Python.

This tutorial explains how to use the two ’operator ** as pow () to calculate powers in Python. illustrated an example of each power calculation method. You now have the knowledge to calculate powers in Python like a pro !

If you’re looking for other learning resources to help you master Python, check out our Python Learning Guide .

👻 Read also: what is the best laptop for engineering students in 2022?

## Javascript Power Function exp: Questions

How do I merge two dictionaries in a single expression (taking union of dictionaries)?

5 answers

By Carl Meyer

I have two Python dictionaries, and I want to write a single expression that returns these two dictionaries, merged (i.e. taking the union). The `update()` method would be what I need, if it returned its result instead of modifying a dictionary in-place.

``````>>> x = {"a": 1, "b": 2}
>>> y = {"b": 10, "c": 11}
>>> z = x.update(y)
>>> print(z)
None
>>> x
{"a": 1, "b": 10, "c": 11}
``````

How can I get that final merged dictionary in `z`, not `x`?

(To be extra-clear, the last-one-wins conflict-handling of `dict.update()` is what I"m looking for as well.)

5839

Answer #1

## How can I merge two Python dictionaries in a single expression?

For dictionaries `x` and `y`, `z` becomes a shallowly-merged dictionary with values from `y` replacing those from `x`.

• In Python 3.9.0 or greater (released 17 October 2020): PEP-584, discussed here, was implemented and provides the simplest method:

``````z = x | y          # NOTE: 3.9+ ONLY
``````
• In Python 3.5 or greater:

``````z = {**x, **y}
``````
• In Python 2, (or 3.4 or lower) write a function:

``````def merge_two_dicts(x, y):
z = x.copy()   # start with keys and values of x
z.update(y)    # modifies z with keys and values of y
return z
``````

and now:

``````z = merge_two_dicts(x, y)
``````

### Explanation

Say you have two dictionaries and you want to merge them into a new dictionary without altering the original dictionaries:

``````x = {"a": 1, "b": 2}
y = {"b": 3, "c": 4}
``````

The desired result is to get a new dictionary (`z`) with the values merged, and the second dictionary"s values overwriting those from the first.

``````>>> z
{"a": 1, "b": 3, "c": 4}
``````

A new syntax for this, proposed in PEP 448 and available as of Python 3.5, is

``````z = {**x, **y}
``````

And it is indeed a single expression.

Note that we can merge in with literal notation as well:

``````z = {**x, "foo": 1, "bar": 2, **y}
``````

and now:

``````>>> z
{"a": 1, "b": 3, "foo": 1, "bar": 2, "c": 4}
``````

It is now showing as implemented in the release schedule for 3.5, PEP 478, and it has now made its way into the What"s New in Python 3.5 document.

However, since many organizations are still on Python 2, you may wish to do this in a backward-compatible way. The classically Pythonic way, available in Python 2 and Python 3.0-3.4, is to do this as a two-step process:

``````z = x.copy()
z.update(y) # which returns None since it mutates z
``````

In both approaches, `y` will come second and its values will replace `x`"s values, thus `b` will point to `3` in our final result.

## Not yet on Python 3.5, but want a single expression

If you are not yet on Python 3.5 or need to write backward-compatible code, and you want this in a single expression, the most performant while the correct approach is to put it in a function:

``````def merge_two_dicts(x, y):
"""Given two dictionaries, merge them into a new dict as a shallow copy."""
z = x.copy()
z.update(y)
return z
``````

and then you have a single expression:

``````z = merge_two_dicts(x, y)
``````

You can also make a function to merge an arbitrary number of dictionaries, from zero to a very large number:

``````def merge_dicts(*dict_args):
"""
Given any number of dictionaries, shallow copy and merge into a new dict,
precedence goes to key-value pairs in latter dictionaries.
"""
result = {}
for dictionary in dict_args:
result.update(dictionary)
return result
``````

This function will work in Python 2 and 3 for all dictionaries. e.g. given dictionaries `a` to `g`:

``````z = merge_dicts(a, b, c, d, e, f, g)
``````

and key-value pairs in `g` will take precedence over dictionaries `a` to `f`, and so on.

## Critiques of Other Answers

Don"t use what you see in the formerly accepted answer:

``````z = dict(x.items() + y.items())
``````

In Python 2, you create two lists in memory for each dict, create a third list in memory with length equal to the length of the first two put together, and then discard all three lists to create the dict. In Python 3, this will fail because you"re adding two `dict_items` objects together, not two lists -

``````>>> c = dict(a.items() + b.items())
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for +: "dict_items" and "dict_items"
``````

and you would have to explicitly create them as lists, e.g. `z = dict(list(x.items()) + list(y.items()))`. This is a waste of resources and computation power.

Similarly, taking the union of `items()` in Python 3 (`viewitems()` in Python 2.7) will also fail when values are unhashable objects (like lists, for example). Even if your values are hashable, since sets are semantically unordered, the behavior is undefined in regards to precedence. So don"t do this:

``````>>> c = dict(a.items() | b.items())
``````

This example demonstrates what happens when values are unhashable:

``````>>> x = {"a": []}
>>> y = {"b": []}
>>> dict(x.items() | y.items())
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unhashable type: "list"
``````

Here"s an example where `y` should have precedence, but instead the value from `x` is retained due to the arbitrary order of sets:

``````>>> x = {"a": 2}
>>> y = {"a": 1}
>>> dict(x.items() | y.items())
{"a": 2}
``````

Another hack you should not use:

``````z = dict(x, **y)
``````

This uses the `dict` constructor and is very fast and memory-efficient (even slightly more so than our two-step process) but unless you know precisely what is happening here (that is, the second dict is being passed as keyword arguments to the dict constructor), it"s difficult to read, it"s not the intended usage, and so it is not Pythonic.

Here"s an example of the usage being remediated in django.

Dictionaries are intended to take hashable keys (e.g. `frozenset`s or tuples), but this method fails in Python 3 when keys are not strings.

``````>>> c = dict(a, **b)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: keyword arguments must be strings
``````

From the mailing list, Guido van Rossum, the creator of the language, wrote:

I am fine with declaring dict({}, **{1:3}) illegal, since after all it is abuse of the ** mechanism.

and

Apparently dict(x, **y) is going around as "cool hack" for "call x.update(y) and return x". Personally, I find it more despicable than cool.

It is my understanding (as well as the understanding of the creator of the language) that the intended usage for `dict(**y)` is for creating dictionaries for readability purposes, e.g.:

``````dict(a=1, b=10, c=11)
``````

instead of

``````{"a": 1, "b": 10, "c": 11}
``````

## Response to comments

Despite what Guido says, `dict(x, **y)` is in line with the dict specification, which btw. works for both Python 2 and 3. The fact that this only works for string keys is a direct consequence of how keyword parameters work and not a short-coming of dict. Nor is using the ** operator in this place an abuse of the mechanism, in fact, ** was designed precisely to pass dictionaries as keywords.

Again, it doesn"t work for 3 when keys are not strings. The implicit calling contract is that namespaces take ordinary dictionaries, while users must only pass keyword arguments that are strings. All other callables enforced it. `dict` broke this consistency in Python 2:

``````>>> foo(**{("a", "b"): None})
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: foo() keywords must be strings
>>> dict(**{("a", "b"): None})
{("a", "b"): None}
``````

This inconsistency was bad given other implementations of Python (PyPy, Jython, IronPython). Thus it was fixed in Python 3, as this usage could be a breaking change.

I submit to you that it is malicious incompetence to intentionally write code that only works in one version of a language or that only works given certain arbitrary constraints.

More comments:

`dict(x.items() + y.items())` is still the most readable solution for Python 2. Readability counts.

My response: `merge_two_dicts(x, y)` actually seems much clearer to me, if we"re actually concerned about readability. And it is not forward compatible, as Python 2 is increasingly deprecated.

`{**x, **y}` does not seem to handle nested dictionaries. the contents of nested keys are simply overwritten, not merged [...] I ended up being burnt by these answers that do not merge recursively and I was surprised no one mentioned it. In my interpretation of the word "merging" these answers describe "updating one dict with another", and not merging.

Yes. I must refer you back to the question, which is asking for a shallow merge of two dictionaries, with the first"s values being overwritten by the second"s - in a single expression.

Assuming two dictionaries of dictionaries, one might recursively merge them in a single function, but you should be careful not to modify the dictionaries from either source, and the surest way to avoid that is to make a copy when assigning values. As keys must be hashable and are usually therefore immutable, it is pointless to copy them:

``````from copy import deepcopy

def dict_of_dicts_merge(x, y):
z = {}
overlapping_keys = x.keys() & y.keys()
for key in overlapping_keys:
z[key] = dict_of_dicts_merge(x[key], y[key])
for key in x.keys() - overlapping_keys:
z[key] = deepcopy(x[key])
for key in y.keys() - overlapping_keys:
z[key] = deepcopy(y[key])
return z
``````

Usage:

``````>>> x = {"a":{1:{}}, "b": {2:{}}}
>>> y = {"b":{10:{}}, "c": {11:{}}}
>>> dict_of_dicts_merge(x, y)
{"b": {2: {}, 10: {}}, "a": {1: {}}, "c": {11: {}}}
``````

Coming up with contingencies for other value types is far beyond the scope of this question, so I will point you at my answer to the canonical question on a "Dictionaries of dictionaries merge".

## Less Performant But Correct Ad-hocs

These approaches are less performant, but they will provide correct behavior. They will be much less performant than `copy` and `update` or the new unpacking because they iterate through each key-value pair at a higher level of abstraction, but they do respect the order of precedence (latter dictionaries have precedence)

You can also chain the dictionaries manually inside a dict comprehension:

``````{k: v for d in dicts for k, v in d.items()} # iteritems in Python 2.7
``````

or in Python 2.6 (and perhaps as early as 2.4 when generator expressions were introduced):

``````dict((k, v) for d in dicts for k, v in d.items()) # iteritems in Python 2
``````

`itertools.chain` will chain the iterators over the key-value pairs in the correct order:

``````from itertools import chain
z = dict(chain(x.items(), y.items())) # iteritems in Python 2
``````

## Performance Analysis

I"m only going to do the performance analysis of the usages known to behave correctly. (Self-contained so you can copy and paste yourself.)

``````from timeit import repeat
from itertools import chain

x = dict.fromkeys("abcdefg")
y = dict.fromkeys("efghijk")

def merge_two_dicts(x, y):
z = x.copy()
z.update(y)
return z

min(repeat(lambda: {**x, **y}))
min(repeat(lambda: merge_two_dicts(x, y)))
min(repeat(lambda: {k: v for d in (x, y) for k, v in d.items()}))
min(repeat(lambda: dict(chain(x.items(), y.items()))))
min(repeat(lambda: dict(item for d in (x, y) for item in d.items())))
``````

In Python 3.8.1, NixOS:

``````>>> min(repeat(lambda: {**x, **y}))
1.0804965235292912
>>> min(repeat(lambda: merge_two_dicts(x, y)))
1.636518670246005
>>> min(repeat(lambda: {k: v for d in (x, y) for k, v in d.items()}))
3.1779992282390594
>>> min(repeat(lambda: dict(chain(x.items(), y.items()))))
2.740647904574871
>>> min(repeat(lambda: dict(item for d in (x, y) for item in d.items())))
4.266070580109954
``````
``````\$ uname -a
Linux nixos 4.19.113 #1-NixOS SMP Wed Mar 25 07:06:15 UTC 2020 x86_64 GNU/Linux
``````

## Resources on Dictionaries

5839

Answer #2

In your case, what you can do is:

``````z = dict(list(x.items()) + list(y.items()))
``````

This will, as you want it, put the final dict in `z`, and make the value for key `b` be properly overridden by the second (`y`) dict"s value:

``````>>> x = {"a":1, "b": 2}
>>> y = {"b":10, "c": 11}
>>> z = dict(list(x.items()) + list(y.items()))
>>> z
{"a": 1, "c": 11, "b": 10}

``````

If you use Python 2, you can even remove the `list()` calls. To create z:

``````>>> z = dict(x.items() + y.items())
>>> z
{"a": 1, "c": 11, "b": 10}
``````

If you use Python version 3.9.0a4 or greater, then you can directly use:

``````x = {"a":1, "b": 2}
y = {"b":10, "c": 11}
z = x | y
print(z)
``````
``````{"a": 1, "c": 11, "b": 10}
``````

5839

Answer #3

An alternative:

``````z = x.copy()
z.update(y)
``````

How to insert newlines on argparse help text?

5 answers

I"m using `argparse` in Python 2.7 for parsing input options. One of my options is a multiple choice. I want to make a list in its help text, e.g.

``````from argparse import ArgumentParser

parser = ArgumentParser(description="test")

parser.add_argument("-g", choices=["a", "b", "g", "d", "e"], default="a",
help="Some option, where
"
" a = alpha
"
" b = beta
"
" g = gamma
"
" d = delta
"
" e = epsilon")

parser.parse_args()
``````

However, `argparse` strips all newlines and consecutive spaces. The result looks like

```~/Downloads:52\$ python2.7 x.py -h
usage: x.py [-h] [-g {a,b,g,d,e}]

test

optional arguments:
-h, --help      show this help message and exit
-g {a,b,g,d,e}  Some option, where a = alpha b = beta g = gamma d = delta e
= epsilon
```

How to insert newlines in the help text?

406

Answer #1

Try using `RawTextHelpFormatter`:

``````from argparse import RawTextHelpFormatter
parser = ArgumentParser(description="test", formatter_class=RawTextHelpFormatter)
``````

Is a Python list guaranteed to have its elements stay in the order they are inserted in?

5 answers

If I have the following Python code

``````>>> x = []
>>> x = x + [1]
>>> x = x + [2]
>>> x = x + [3]
>>> x
[1, 2, 3]
``````

Will `x` be guaranteed to always be `[1,2,3]`, or are other orderings of the interim elements possible?

366

Answer #1

Yes, the order of elements in a python list is persistent.

Inserting image into IPython notebook markdown

5 answers

I am starting to depend heavily on the IPython notebook app to develop and document algorithms. It is awesome; but there is something that seems like it should be possible, but I can"t figure out how to do it:

I would like to insert a local image into my (local) IPython notebook markdown to aid in documenting an algorithm. I know enough to add something like `<img src="image.png">` to the markdown, but that is about as far as my knowledge goes. I assume I could put the image in the directory represented by 127.0.0.1:8888 (or some subdirectory) to be able to access it, but I can"t figure out where that directory is. (I"m working on a mac.) So, is it possible to do what I"m trying to do without too much trouble?

277

Answer #1

Most of the answers given so far go in the wrong direction, suggesting to load additional libraries and use the code instead of markup. In Ipython/Jupyter Notebooks it is very simple. Make sure the cell is indeed in markup and to display a image use:

``````![alt text](imagename.png "Title")
``````

Further advantage compared to the other methods proposed is that you can display all common file formats including jpg, png, and gif (animations).

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