How I can find the right path in Python Selenium?

I can get it if I use text without space after dot

text()='Derzeit nicht verfügbar.'

But sometimes it is simpler to check if it contains expected text.

contains(text(), 'Derzeit nicht verfügbar.')

Testing example

from selenium import webdriver

html = '''
<span class="a-size-medium a-color-price">Derzeit nicht verfügbar.</span>
<span class="a-size-medium a-color-price">Derzeit nicht verfügbar. </span>
<span class="a-size-medium a-color-price"> Derzeit nicht verfügbar. </span>

<div id="availability" class="a-section a-spacing-none }">
<span class="a-size-medium a-color-price">

Derzeit nicht verfügbar. 

<div id="all-offers-display" class="a-section">
Other text
'''

driver = webdriver.Firefox()
driver.get("data:text/html;charset=utf-8," + html)

print('\n--- Example 1 - with space ---\n')

all_items = driver.find_elements_by_xpath("//span[@class='a-size-medium a-color-price' and text()='Derzeit nicht verfügbar. ']")
for item in all_items:
    print(item.text)
    print('---')

print('\n--- Example 2 - without space ---\n')

all_items = driver.find_elements_by_xpath("//span[@class='a-size-medium a-color-price' and text()='Derzeit nicht verfügbar.']")
for item in all_items:
    print(item.text)
    print('---')

print('\n--- Example 3 - contains ---\n')

all_items = driver.find_elements_by_xpath("//span[@class='a-size-medium a-color-price' and contains(text(), 'Derzeit nicht verfügbar.')]")
for item in all_items:
    print(item.text)
    print('---')