Question

I have a Latex Table that for weekly lesson plans, I want to pull data from syllabi that I will store as lists.(They will be read in from csv) So the syllabus is a list of 50 chapters and the latex has spaces for 2 lessons a week for 4th grade and 3 for sixth, I want to chomp the first lesson and stick in in the first token, then the next . . .
right now my code would just give me chapter1 on Monday, Wed and Fri instead of ch1, ch2, ch3

math6 = ['chapter1', 'chapter2', 'chapter3', 'chapter1-3test']
math4= ['chapter1.1', 'chapter1.2-3', 'chapter2']

    \begin{tabular}{|p{0.7in}|p{0.8in}|p{2.2in}|p{.9in}|p{2.6in}|p{1.6in}|}
    6${}^{th}$ Math  \newline M\newline  & _math6_& 
    6${}^{th}$ Math  \newline W \newline  & _math6_ & 
    6${}^{th}$ Math  \newline  F \newline  & _math6_ &  
    4${}^{th}$ Math  \newline M\newline  &  & _math4_  &
    4${}^{th}$ Math \newline W\newline  &  & _math4_  & 
    \end{tabular}

here is the python

import re
template = file('file1.txt', 'r').read()

lost= ["geography", "physics", "hairdressing", "torah"]
n =0
while n<len(lost):
    temp=lost[n]
    page= re.sub(r'_thing_', temp, template)
    print page
    n+=1
#page= re.sub(r'_thing_', "martha", template)
#file('result.txt', 'w').write(page)

which gives me

#contents of file1
# Really long Latex
#File that has
# geography, geography, mary, tom, susan, geography
#that I want to replace
#read file1 in as a string, replace, save again

#contents of file1
# Really long Latex
#File that has
# physics, physics, mary, tom, susan, physics
#that I want to replace
#read file1 in as a string, replace, save again

#contents of file1
# Really long Latex
#File that has
# hairdressing, hairdressing, mary, tom, susan, hairdressing
#that I want to replace
#read file1 in as a string, replace, save again

#contents of file1
# Really long Latex
#File that has
# torah, torah, mary, tom, susan, torah
#that I want to replace
#read file1 in as a string, replace, save again

Answer 1

The problem with using

re.sub(r'_thing_', temp, template)

is that every occurrence of _thing_ is getting replaced with the same value, temp.

What we desire for here is a temp value that can change with each match.

re.sub provides such a facility through the use of a callback function as the second argument, rather than a string like temp.

The callback is simply a function that takes one argument, the match object, and returns the string we desire for that match.

def replacer(match):
    return ...

Now what to put in place of the ellipsis? We can use an iter here:

In [27]: math6 = ['chapter1', 'chapter2', 'chapter3', 'chapter1-3test']

In [28]: math6 = iter(math6)

In [29]: next(math6)
Out[29]: 'chapter1'

In [30]: next(math6)
Out[30]: 'chapter2'

So what we really want is a callback that looks like this:

def replacer(match):
    return next(data)

But we have more than one set of data: math6 and math4, for example. So we need a callback factory: a function that returns a callback given data:

def replace_with(data):
    def replacer(match):
        return next(data)
    return replacer

---

Putting it all together,

import re

math6 = iter(['chapter1', 'chapter2', 'chapter3', 'chapter1-3test'])
math4 = iter(['chapter1.1', 'chapter1.2-3', 'chapter2'])

text = r'''
    \begin{tabular}{|p{0.7in}|p{0.8in}|p{2.2in}|p{.9in}|p{2.6in}|p{1.6in}|}
    6${}^{th}$ Math  \newline M\newline  & _math6_& 
    6${}^{th}$ Math  \newline W \newline  & _math6_ & 
    6${}^{th}$ Math  \newline  F \newline  & _math6_ &  
    4${}^{th}$ Math  \newline M\newline  &  & _math4_  &
    4${}^{th}$ Math \newline W\newline  &  & _math4_  & 
    \end{tabular}
'''

def replace_with(data):
    def replacer(match):
        return next(data)
    return replacer

for pat, data in [(r'_math6_', math6), (r'_math4_', math4)]:
    text = re.sub(pat, replace_with(data), text)

print(text)    

yields

\begin{tabular}{|p{0.7in}|p{0.8in}|p{2.2in}|p{.9in}|p{2.6in}|p{1.6in}|}
6${}^{th}$ Math  \newline M\newline  & chapter1& 
6${}^{th}$ Math  \newline W \newline  & chapter2 & 
6${}^{th}$ Math  \newline  F \newline  & chapter3 &  
4${}^{th}$ Math  \newline M\newline  &  & chapter1.1  &
4${}^{th}$ Math \newline W\newline  &  & chapter1.2-3  & 
\end{tabular}