Py for Network Engineers: Day 2 String

String overview

Strings are ordered immutable sequence of caracteres linke “Rafael”.

In [1]: name = 'Rafael'
In [2]: name[0]
Out[2]: 'R'
In [3]: list(bytes(name, "utf-8"))
Out[3]: [82, 97, 102, 97, 101, 108]
In [4]: chr(82)
Out[4]: 'R'
In [5]: chr(97)
Out[5]: 'a'

The string ‘Rafael’ has a conjunction of five characters on each position as shown above. Among many tables for characters those most famous are ASCII (128 positions) and UTF8 (120 mil characters).

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Docstring allows us put notes, comments spread over many lines:

"""
Doctstring

multiline

comments.
"""

"""Demo of pushing configurations"""
commands = "router ospf 1\n router-id 1.1.1.1\n networ 192.168.1.0 0.0.0.255 area 0\n"
print(commands)

router ospf 1
router-id 1.1.1.1
networ 192.168.1.0 0.0.0.255 area 0

Converting string

Someting converts strings into intergers and vice verse is useful.

In [1]: my_number = "4"
In [2]: type(my_number)
Out[2]: str
In [3]: 3 * my_number
Out[3]: '444'
In [4]: my_new_number = 4
In [5]: type(my_new_number)
Out[5]: int
In [6]: 3 * my_new_number
Out[6]: 12
In [7]: version = '15'
In [8]: string_new_number = str(my_new_number)
In [9]: type(string_new_number)
Out[9]: str
In [10]: print(string_new_number)
4
In [11]: float_number = float(my_new_number)
In [12]: print(float_number)
4.0
In [13]: type(float_number)
Out[13]: float

#! /usr/bin/env python3

version = "15"
interger_version = int(version)

if interger_version > 12:
print("VERSION CHECK PASSED")
else:
print("VERSION CHECK FAILED.")

❯ python3 version_test.py
VERSION CHECK PASSED

Input function

Input function as a way to dynamically accept user’s input and by default inputs are strings.

#!/usr/bin/env python3

show_command = input("Enter the show command you wish to execute: ")
print(show_command)

❯ python3 input_check.py
Enter the show command you wish to execute: sh interface b
sh interface b

Concatenation

keep in mind that concatenation must only work between strings

In [1]: greeting = "Hello my name is Rafael and my age is "
In [2]: age = 18
In [3]: type(greeting)
Out[3]: str
In [4]: type(age)
Out[4]: int

In [5]: print(greeting + age)
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
TypeError Traceback (most recent call last)
Cell In[5], line 1
 - → 1 print(greeting + age)
TypeError: can only concatenate str (not "int") to str

In [6]: print(greeting + str(age))
Hello my name is Rafael and my age is 18

#!/usr/bin/env python3

command_string = input("Enter the command you wish to send to the device: ")
commands_to_send = "enable\n" + command_string + "\n"

print(commands_to_send)

❯ python3 concat_example.py
Enter the command you wish to send to the device: show vrf MGMT ip route
enable
show vrf MGMT ip route

Formatting strings

“Old” Style — Place holder

#!/usr/bin/env python3

name = input("What's your name? ")
age = input("what's your age? ")
massage1 = "Message 1: Hello {fname}, your age is {fage}".format(fname=name, fage=age)

print(massage1)

#Able to use index

message2 = "Message 2: Hello {}, your age is {}".format(name, age)
print(message3)

message3 = "Message 3: Hello {1}, your age is {0}".format(name, age)
print(message2)

❯ python3 format_example1.py
What's your name? CCIE
what's your age? 67796
Message 1: Hello CCIE, your age is 67796
Message 2: Hello CCIE, your age is 67796
Message 1: Hello 67796, your age is CCIE

“new” Style — F-String

#!/usr/bin/env python3

device_name = "R1"
version_number = "15.8"

print(f"The device name is {device_name} and the version is {version_number}")

❯ python3 fstring_example.py
The device name is R1 and the version is 15.8

String methods

In [1]: platform = 'Cisco_xe'
In [2]: platform. #hit tab
capitalize() format() isidentifier() ljust() rfind() startswith()
casefold() format_map() islower() lower() rindex() strip()
center() index() isnumeric() lstrip() rjust() swapcase()
count() isalnum() isprintable() maketrans() rpartition() title()
encode() isalpha() isspace() partition() rsplit() translate()
endswith() isascii() istitle() removeprefix() rstrip() upper()
expandtabs() isdecimal() isupper() removesuffix() split() zfill()
find() isdigit() join() replace() splitlines()
In [2]: upper_platform = platform.upper()
In [3]: upper_platform
Out[3]: 'CISCO_XE'

In [13]: interface = "GigabitEthernet0/2"
In [14]: interface.startswith("Fast")
Out[14]: False
In [15]: interface.startswith("Gigabit")
Out[15]: True
In [16]: if interface.startswith('Giga'):
…: print("This is a GigabitEthernet Interface")
…:
This is a GigabitEthernet Interface

#!/usr/bin/env python3

platform = input("What's your platform? ")
# show_command = input("what show command do you want to send? ").lower()
show_command = input("what show command do you want to send? ")
platform_to_test = platform.lower()

if platform_to_test == "cisco":
command_to_send = f"enable\n{show_command}\n"

print("-" * 30, "Sending commands")
print(command_to_send)

❯ python3 string_method_example.py
What's your platform? Cisco
what show command do you want to send? show ip interface brief
 - - - - - - - - - - - - - - - Sending commands
enable
show ip interface brief

$WHOAMI

https://www.linkedin.com/in/rafaesil

What's Next

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