Dictionary Comprehensions | Dictionary in Python | Coding Winds

Dictionary Comprehension

Hello guys, here we will talk about dictionary comprehension.

Dictionary comprehension is a precise way to create a new dictionary from the existing dictionary in python

Syntax is,

{key: expression for x in iterable if conditional}

Output

Another example,

Output

Single If statement

Output

We see that the conditional statement worked properly.

Similarly we can use multiple If loop and if-else also.

Nested dictionary with two dictionary comprehensions

Output

This code without dictionary comprehension will look like this,

We must be careful while using dictionary comprehension as:

1)     They can sometimes make the code run slower and consume more memory.

2)     They can also decrease the readability of the code.

  Hello Python people, for this blog we have taken help from the book Python : The Complete Reference.

Hope all your doubts regarding this are clear now.

If you still have any doubt on this topic then do come to us via email "sophomoretechs@gmail.com" or via Instagram "@coding.winds".

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Dynamic Memory Allocation | malloc() | calloc() | free () | realloc() | Array of undefined size | Changing the size of an array using realloc() | CODING WINDS

  Dynamic Memory Allocation

 

Hey people in this blog you are going to read about “Dynamic Memory Allocation”, you need to know before you are using functions like “malloc()”, “calloc()”, “free()”, etc. in your C/C++ code.

To change or define the size of any data structure during the runtime is called “Dynamic Memory Allocation”.

To use Dynamic memory allocation we need to use several library functions

malloc() , calloc() , free() , realloc().  These operations are including in the library <stdlib.h> .

1.  malloc() function :

The name “malloc” stands for memory allocation.

SYNTAX  :  ptr = (CastType *)malloc(size);

The malloc() function reserves a block of memory of the specified number of bytes. And, it returns a pointer of void which can be casted into pointers of any form.

2.  calloc() function :

The name “calloc” stands for contiguous allocation.

The malloc() function allocates memory and leaves the memory uninitialized. Whereas, the calloc() function allocates memory and initializes all bits to zero.

 

SYNTAX  :  ptr = (CastType *)calloc(n,elements_size);

Where, n – number of elements

3.  free() function :

The dynamically allocated memory created either with either calloc() or malloc() does not get freed upon themselves. You must  explicitly use free() to release the space.

SYNTAX  :  free(ptr);

4.  realloc() function :

The name “realloc” stands for re-allocation.

“realloc” method in C is used to dynamically change the memory allocation of a previously allocated memory. In other words, if the memory previously allocated with the help of “malloc” or “calloc” is insufficient, “realloc” can be used to dynamically re-allocate memory. Re-allocation of memory maintains the already present value and new blocks will be initialized with default garbage value.

 

SYNTAX  :  ptr = realloc(ptr, NewSize);

 

It is hard to understand this topic by just reading this bookish deifinition.

So, let’s just look into some working examples of this, which might help get insight of this topic in a better way :

1.    Declaring an array of a variable size, using “malloc()“ function.

2.    Intializing an array of variable size with a zero value, using “calloc()” function.

3.    Deleting a memory space occupied by any data structure, using “free()” function.

4.    Re-defining the size of an array, using “realloc()”  function.

 

 

1.   Declaring an array of a variable size, using “malloc()“ function.

 

 

2.   Intializing an array of variable size with a zero value, using “calloc()” function.

 

 

3.   Deleting a memory space occupied by any data structure, using “free()” function.

 

4.   Re-defining the size of an array, using “realloc()”  function.