Q:

Magento 2 : Issue With Override Magento\Checkout\Model\Session

i am override the checkout model seesion in this way in magento 2.2.5
"\app\code\Namespace\Modulename\etc\di.xml"
<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">

    <preference for="Magento\Checkout\Model\Session" type="Namespace\Modulename\Model\Session" />

</config>

and crested file like 
app/code/Namespace/Modulename/Model/Session.php
namespace Namespace\Modulename\Model;

class Session extends \Magento\Checkout\Model\Session
{
    protected $_checkoutSession;

    public function __construct(        
    \Magento\Checkout\Model\Session $checkoutSession
    ) {

    $this->_checkoutSession = $checkoutSession;

    }

    /**
     * Get checkout quote instance by current session
     *
     * @return Quote
     * @SuppressWarnings(PHPMD.CyclomaticComplexity)
     * @SuppressWarnings(PHPMD.NPathComplexity)
     */
    public function getQuote()
    {
        $this->_eventManager->dispatch('custom_quote_process', ['checkout_session' => $this]);
    die("quote");
        if ($this->_quote === null) {
            $quote = $this->quoteFactory->create();
        die($this->getQuoteId());
            if ($this->getQuoteId()) {
                try {
                    if ($this->_loadInactive) {
                        $quote = $this->quoteRepository->get($this->getQuoteId());
                    } else {
                        $quote = $this->quoteRepository->getActive($this->getQuoteId());
                    }

                    /**
                     * If current currency code of quote is not equal current currency code of store,
                     * need recalculate totals of quote. It is possible if customer use currency switcher or
                     * store switcher.
                     */
                    if ($quote->getQuoteCurrencyCode() != $this->_storeManager->getStore()->getCurrentCurrencyCode()) {
                        $quote->setStore($this->_storeManager->getStore());
                        $this->quoteRepository->save($quote->collectTotals());
                        /*
                         * We mast to create new quote object, because collectTotals()
                         * can to create links with other objects.
                         */
                        $quote = $this->quoteRepository->get($this->getQuoteId());
                    }
                } catch (\Magento\Framework\Exception\NoSuchEntityException $e) {
                    $this->setQuoteId(null);
                }
            }

            if (!$this->getQuoteId()) {
                if ($this->_customerSession->isLoggedIn() || $this->_customer) {
                    $customerId = $this->_customer
                        ? $this->_customer->getId()
                        : $this->_customerSession->getCustomerId();
                    try {
                        $quote = $this->quoteRepository->getActiveForCustomer($customerId);
                        $this->setQuoteId($quote->getId());
            $quote->getShippingAddress()->setPostcode('7879122');
            $quote->save();
                    } catch (\Magento\Framework\Exception\NoSuchEntityException $e) {
                    }
                } else {
                    $quote->setIsCheckoutCart(true);
                    $this->_eventManager->dispatch('checkout_quote_init', ['quote' => $quote]);
                }
            }

            if ($this->_customer) {
                $quote->setCustomer($this->_customer);
            } elseif ($this->_customerSession->isLoggedIn()) {
                $quote->setCustomer($this->customerRepository->getById($this->_customerSession->getCustomerId()));
            }

            $quote->setStore($this->_storeManager->getStore());
            $this->_quote = $quote;
        }

        if (!$this->isQuoteMasked() && !$this->_customerSession->isLoggedIn() && $this->getQuoteId()) {
            $quoteId = $this->getQuoteId();
            /** @var $quoteIdMask \Magento\Quote\Model\QuoteIdMask */
            $quoteIdMask = $this->quoteIdMaskFactory->create()->load($quoteId, 'quote_id');
            if ($quoteIdMask->getMaskedId() === null) {
                $quoteIdMask->setQuoteId($quoteId)->save();
            }
            $this->setIsQuoteMasked(true);
        }

        $remoteAddress = $this->_remoteAddress->getRemoteAddress();
        if ($remoteAddress) {
            $this->_quote->setRemoteIp($remoteAddress);
            $xForwardIp = $this->request->getServer('HTTP_X_FORWARDED_FOR');
            $this->_quote->setXForwardedFor($xForwardIp);
        }

        return $this->_quote;
    }
}

and i clear the cache but i got an error like below
1 exception(s):

Exception #0 (LogicException): Circular dependency: Namespace\Modulename\Model\Session depends on Namespace\Modulename\Model\Session and vice versa.

any solution for that

A:

try this code.
namespace Namespace\Modulename\Model;

class Session extends \Magento\Checkout\Model\Session
{
    /**
     * Get checkout quote instance by current session
     *
     * @return Quote
     * @SuppressWarnings(PHPMD.CyclomaticComplexity)
     * @SuppressWarnings(PHPMD.NPathComplexity)
     */
    public function getQuote()
    {
        $this->_eventManager->dispatch('custom_quote_process', ['checkout_session' => $this]);
    die("quote");
        if ($this->_quote === null) {
            $quote = $this->quoteFactory->create();
        die($this->getQuoteId());
            if ($this->getQuoteId()) {
                try {
                    if ($this->_loadInactive) {
                        $quote = $this->quoteRepository->get($this->getQuoteId());
                    } else {
                        $quote = $this->quoteRepository->getActive($this->getQuoteId());
                    }

                    /**
                     * If current currency code of quote is not equal current currency code of store,
                     * need recalculate totals of quote. It is possible if customer use currency switcher or
                     * store switcher.
                     */
                    if ($quote->getQuoteCurrencyCode() != $this->_storeManager->getStore()->getCurrentCurrencyCode()) {
                        $quote->setStore($this->_storeManager->getStore());
                        $this->quoteRepository->save($quote->collectTotals());
                        /*
                         * We mast to create new quote object, because collectTotals()
                         * can to create links with other objects.
                         */
                        $quote = $this->quoteRepository->get($this->getQuoteId());
                    }
                } catch (\Magento\Framework\Exception\NoSuchEntityException $e) {
                    $this->setQuoteId(null);
                }
            }

            if (!$this->getQuoteId()) {
                if ($this->_customerSession->isLoggedIn() || $this->_customer) {
                    $customerId = $this->_customer
                        ? $this->_customer->getId()
                        : $this->_customerSession->getCustomerId();
                    try {
                        $quote = $this->quoteRepository->getActiveForCustomer($customerId);
                        $this->setQuoteId($quote->getId());
            $quote->getShippingAddress()->setPostcode('7879122');
            $quote->save();
                    } catch (\Magento\Framework\Exception\NoSuchEntityException $e) {
                    }
                } else {
                    $quote->setIsCheckoutCart(true);
                    $this->_eventManager->dispatch('checkout_quote_init', ['quote' => $quote]);
                }
            }

            if ($this->_customer) {
                $quote->setCustomer($this->_customer);
            } elseif ($this->_customerSession->isLoggedIn()) {
                $quote->setCustomer($this->customerRepository->getById($this->_customerSession->getCustomerId()));
            }

            $quote->setStore($this->_storeManager->getStore());
            $this->_quote = $quote;
        }

        if (!$this->isQuoteMasked() && !$this->_customerSession->isLoggedIn() && $this->getQuoteId()) {
            $quoteId = $this->getQuoteId();
            /** @var $quoteIdMask \Magento\Quote\Model\QuoteIdMask */
            $quoteIdMask = $this->quoteIdMaskFactory->create()->load($quoteId, 'quote_id');
            if ($quoteIdMask->getMaskedId() === null) {
                $quoteIdMask->setQuoteId($quoteId)->save();
            }
            $this->setIsQuoteMasked(true);
        }

        $remoteAddress = $this->_remoteAddress->getRemoteAddress();
        if ($remoteAddress) {
            $this->_quote->setRemoteIp($remoteAddress);
            $xForwardIp = $this->request->getServer('HTTP_X_FORWARDED_FOR');
            $this->_quote->setXForwardedFor($xForwardIp);
        }

        return $this->_quote;
    }
}

