Why can't I upgrade to Php 7 on debian?

Question

linux

Unable to upgrade php 5.4 to 7.0
Actions:
1. [email protected]:~# add-apt-repository ppa:ondrej/php
2. [email protected]:~# apt-get update
3.

[email protected]:~# apt-get install php7.0                                                             
Reading package lists... Done                                                                         
Building dependency tree                                                                              
Reading state information... Done                                                                     
Note, selecting 'php7.0-cli' for regex 'php7.0'                                                       
0 upgraded, 0 newly installed, 0 to remove and 36 not upgraded.                                       
[email protected]:~#

What else can be done?
Additional info:

[email protected]:~# apt-get install php7.0 php-pear                                                      
Reading package lists... Done                                                                           
Building dependency tree                                                                                
Reading state information... Done                                                                       
Some packages could not be installed. This may mean that you have                                       
requested an impossible situation or if you are using the unstable                                      
distribution that some required packages have not yet been created                                      
or been moved out of Incoming.                                                                          
The following information may help to resolve the situation:                                            
                                                                                                        
The following packages have unmet dependencies:                                                         
 php7.0 : Depends: libapache2-mod-php7.0 but it is not going to be installed or                         
                   php7.0-fpm but it is not going to be installed or                                    
                   php7.0-cgi but it is not going to be installed                                       
          Depends: php7.0-common but it is not going to be installed                                    
E: Unable to correct problems, you have held broken packages.

Answer 1

The turnip PPAs are for Ubuntu. Do not make Frankenstein out of the system and install from testing.
"you have held broken packages" just means that you have FrankenDebian, that is, turnips for different releases. Upgrade the whole system to Stretch and don't suffer.
https://wiki.debian.org/DontBreakDebian

# apt-cache policy php7.0
php7.0:
  Installed: 7.0.6-13
  Candidate: 7.0.13-2
  Version table:
     7.0.13-2 0
        500 http://mirror.yandex.ru/debian/ testing/main amd64 Packages
 *** 7.0.6-13 0
        100 /var/lib/dpkg/status

# cat /etc/apt/sources.list.d/debian-testing.list 
deb      "http://mirror.yandex.ru/debian/" testing non-free main