Generate a Unique String in Python/Django

Question

What I want is to generate a string(key) of size 5 for my users on my website. More like a BBM PIN.

The key will contain numbers and uppercase English letters:

Answer 1

I have a unique field, named 'systemCode' within a lot of my models. And I am generating this manually, but also sometimes it can take value from user input, so I have to check this value before saving and if it matches , regenerating this value as a unique value.

And this is how I generate unique strings at this scenario :

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This is my standard class Model :

class ClassOne(models.Model):
   name = models.CharField(max_length=100)
   systemCode = models.CharField(max_length=25, blank=True, null=True, unique=True)
   ....

I am using save() method to generate and check this systemCode is unique :

    def save(self, *args, **kwargs):
        systemCode = self.systemCode
        if not systemCode:
            systemCode = uuid.uuid4().hex[:6].upper()
        while ClassOne.objects.filter(systemCode=systemCode).exclude(pk=self.pk).exists():
            systemCode = uuid.uuid4().hex[:6].upper()
        self.systemCode = systemCode
        super(ClassOne, self).save(*args, **kwargs)

But I have same systemCode field in all my Models. So I am using a function to generate value.

So, this is how to generate unique value for all models using saveSystemCode() function :

import uuid 

def saveSystemCode(inClass, inCode, inPK, prefix):
    systemCode = inCode
    if not systemCode:
        systemCode = uuid.uuid4().hex[:6].upper()

    while inClass.objects.filter(systemCode=systemCode).exclude(pk=inPK).exists():
        systemCode = uuid.uuid4().hex[:6].upper()

    return systemCode

class ClassOne(models.Model):
    name = models.CharField(max_length=100)
    systemCode = models.CharField(max_length=25, blank=True, null=True, unique=True)
    ....

    def save(self, *args, **kwargs):
        self.systemCode = saveSystemCode(ClassOne, self.systemCode, self.pk, 'one_')
        super(ClassOne, self).save(*args, **kwargs)


class ClassTwo(models.Model):
    name = models.CharField(max_length=100)
    systemCode = models.CharField(max_length=25, blank=True, null=True, unique=True)
    ....

    def save(self, *args, **kwargs):
        self.systemCode = saveSystemCode(ClassTwo, self.systemCode, self.pk, 'two_')
        super(ClassTwo, self).save(*args, **kwargs)

class ClassThree(models.Model):
    name = models.CharField(max_length=100)
    systemCode = models.CharField(max_length=25, blank=True, null=True, unique=True)
    ....

    def save(self, *args, **kwargs):
        self.systemCode = saveSystemCode(ClassThree, self.systemCode, self.pk, 'three_')
        super(ClassThree, self).save(*args, **kwargs)

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while loop in the 'saveSystemCode' function is preventing to save same value again.