Cara menggunakan modify function in python

You can run Python code in AWS Lambda. Lambda provides runtimes for Python that run your code to process events. Your code runs in an environment that includes the SDK for Python [Boto3], with credentials from an AWS Identity and Access Management [IAM] role that you manage.

Lambda supports the following Python runtimes.

Python

The runtime information in this table undergoes continuous updates. For more information on using AWS SDKs in Lambda, see Managing AWS SDKs in Lambda functions.

To create a Python function

1. Open the Lambda console.

2. Choose Create function.

3. Configure the following settings:

   • Name – my-function.

   • Runtime – Python 3.9.

   • Role – Choose an existing role.

   • Existing role – lambda-role.

4. Choose Create function.

5. To configure a test event, choose Test.

6. For Event name, enter test.

7. Choose Save changes.

8. To invoke the function, choose Test.

The console creates a Lambda function with a single source file named lambda_function. You can edit this file and add more files in the built-in code editor. To save your changes, choose Save. Then, to run your code, choose Test.

The Lambda console uses AWS Cloud9 to provide an integrated development environment in the browser. You can also use AWS Cloud9 to develop Lambda functions in your own environment. For more information, see Working with Lambda Functions in the AWS Cloud9 user guide.

To get started with application development in your local environment, deploy one of the sample applications available in this guide's GitHub repository.

Sample Lambda applications in Python

• blank-python – A Python function that shows the use of logging, environment variables, AWS X-Ray tracing, layers, unit tests and the AWS SDK.

Your Lambda function comes with a CloudWatch Logs log group. The function runtime sends details about each invocation to CloudWatch Logs. It relays any logs that your function outputs during invocation. If your function returns an error, Lambda formats the error and returns it to the invoker.

Topics

• Lambda function handler in Python
• Deploy Python Lambda functions with .zip file archives
• Deploy Python Lambda functions with container images
• AWS Lambda context object in Python
• AWS Lambda function logging in Python
• AWS Lambda function errors in Python
• Instrumenting Python code in AWS Lambda

If you try to mutate a sequence while traversing through it, Python usually doesn't complain. For example:

Table of Contents

• What about dictionaries¶
• Resources¶
• How do you change the position of a list in Python?
• How do you modify a list in Python?
• Can lists be modified?
• How do I update a nested list in Python?

# src.py

l = [3, 4, 56, 7, 10, 9, 6, 5]

for i in l:
    if not i % 2 == 0:
        continue
    l.remove[i]

print[l]

The above snippet iterates through a list of numbers and modifies the list l in-place to remove any even number. However, running the script prints out this:

Wait a minute! The output doesn't look correct. The final list still contains 56 which is an even number. Why did it get skipped? Printing the members of the list while the for-loop advances reveal what's happening inside:

3
4
7
10
6
[3, 56, 7, 9, 5]

From the output, it seems like the for-loop doesn't even visit all the elements of the sequence. However, trying to emulate what happens inside the for-loop with iter and next makes the situation clearer. Notice the following example. I'm using ipython shell to explore:

In [1]: l = [3, 4, 56, 7, 10, 9, 6, 5]

In [2]: # Make the list an iterator.

In [3]: it = iter[l]

In [4]: # Emulate for-loop by applying 'next[]' function on 'it'.

In [5]: next[it]
Out[5]: 3

In [6]: next[it]
Out[6]: 4

In [7]: # Remove a value that's already been visited by the iterator.

In [8]: l.remove[3]

In [9]: next[it]
Out[9]: 7

In [10]: # Notice how the iterator skipped 56. Remove another.

In [11]: l.remove[4]

In [12]: next[it]
Out[12]: 9

The REPL experiment reveals that

Whenever you remove an element of an iterable that's already been visited by the iterator, in the next iteration, the iterator will jump right by 1 element. This can make the iterator skip a value. The opposite is also true if you prepend some value to a sequence after the iterator has started iterating. In that case, in the next iteration, the iterator will jump left by 1 element and may visit the same value again.

Here's what happens when you prepend values after the iteration has started:

In[1]: l = [3, 4, 56, 7, 10, 9, 6, 5]

In[2]: it = iter[l]

In[3]: next[it]
Out[3]: 3

In[4]: next[it]
Out[4]: 4

In[5]: l.insert[0, 44]

In[6]: next[it]
Out[6]: 4

Notice how the element 4 is being visited twice after prepending a value to the list l.

Solution¶

To solve this, you'll have to make sure the target elements don't get removed after the iterator has already visited them. You can iterate in the reverse order and remove elements maintaining the original order. The first snippet can be rewritten as follows:

# src.py

l = [3, 4, 56, 7, 10, 9, 6, 5]

# Here, 'reversed' returns a lazy iterator, so it's performant!
for i in reversed[l]:
    print[i]
    if not i % 2 == 0:
        continue
    l.remove[i]

print[l]

Running the script prints:

5
6
9
10
7
56
4
3
[3, 7, 9, 5]

Notice, how the iterator now visits all the elements and the final list contains the odd elements as expected.

Another way you can solve this is—by copying the list l before iterating. But this can be expensive if l is large:

# src.py
l = [3, 4, 56, 7, 10, 9, 6, 5]

# Here 'l.copy[]' creates a shallow copy of 'l'. It's
# less performant than 'reversed[l]'.
for i in l.copy[]:
    print[i]
    if not i % 2 == 0:
        continue
    l.remove[i]

print[l]

This time, the order of the iteration and element removal is the same, but that isn't a problem since these two operations occur on two different lists. Running the snippet produces the following output:

3
4
56
7
10
9
6
5
[3, 7, 9, 5]

What about dictionaries¶

Dictionaries don't even allow you to change their sizes while iterating. The following snippet raises a RuntimeError:

# src.py

# {0: 0, 1: 1, 2: 2, 3: 3, 4: 4, 5: 5, 6: 6, 7: 7, 8: 8, 9: 9}
d = {k: k for k in range[10]}

for k, v in d.items[]:
    if not v % 2 == 0:
        continue
    d.pop[k]

Traceback [most recent call last]:
  File "/home/rednafi/canvas/personal/reflections/src.py", line 4, in 
    for k,v in d.items[]:
RuntimeError: dictionary changed size during iteration

You can solve this by making a copy of the keys of the dictionary and iterating through it while removing the elements from the dictionary. Here's one way to do it:

# src.py

# {0: 0, 1: 1, 2: 2, 3: 3, 4: 4, 5: 5, 6: 6, 7: 7, 8: 8, 9: 9}
d = {k: k for k in range[10]}

# This creates a copy of all the keys of 'd'.
# At least we arent't creating a new copy of the
# entire dict and tuple creation is quite fast.
for k in tuple[d.keys[]]:
    if not d[k] % 2 == 0:
        continue
    d.pop[k]

print[d]

Running the snippet prints:

{1: 1, 3: 3, 5: 5, 7: 7, 9: 9}

Voila, the key-value pairs of the even numbers have been removed successfully!

Resources¶

I wrote this post after watching Anthony Sottile's short YouTube video on the topic. Go watch it.

How do you change the position of a list in Python?

Method #1 : Using append[] + pop[] + index[] This particular functionality can be performed in one line by combining these functions. The append function adds the element removed by pop function using the index provided by index function.

How do you modify a list in Python?

List in python is mutable types which means it can be changed after assigning some value. The list is similar to arrays in other programming languages..

Change first element mylist[0]=value..

Change third element mylist[2]=value..

Change fourth element mylist[3]=value..

Can lists be modified?

And while most of the data types we've worked with in introductory Python are immutable [including integers, floats, strings, Booleans, and tuples], lists and dictionaries are mutable. That means a global list or dictionary can be changed even when it's used inside of a function, just like we saw in the examples above.

How do I update a nested list in Python?

To add new values to the end of the nested list, use append[] method. When you want to insert an item at a specific position in a nested list, use insert[] method. You can merge one list into another by using extend[] method. If you know the index of the item you want, you can use pop[] method.